HIGHLANDS RANCH, Colo. – It happened in that eerie, dreamlike space after the Twin Towers collapsed.

People were shuffling through downtown San Diego in a daze, and kept glancing up at the city’s gleaming Pan-Pacific high-rises, prepared to cower or run if airplanes suddenly began tearing through glass and steel in massive, orange fireballs.

Commercial flights that had been swooping regularly into San Diego International Airport were grounded, and the only sounds were the thwap-thwap of Navy choppers and the bellows of foghorns from ships mobilizing across the bay to protect the U.S.-Mexico border.

The legendary naval city was on unprecedented high alert, and the air was thick with fear and panic. As a nation, we were grappling with a media-generated, collective case of post-traumatic stress disorder, and it seemed like anything could happen, even in sunny southern California.

We all remember where were were on Sept. 11, 2001, but something a bit more mundane, a tense situation caused by a single woman on a London tram recently, reminded me of that sad day in vivid detail.

While terrorists were crashing airlines into buildings, a grungy stranger on a San Diego street was hurling racial slurs at me like Molotov cocktails. Hatred ruled on both coasts that day, just as it did recently on a public tram in London.

I remember 9/11 quite well. I was heading back to the San Diego Convention Center to file a story on deadline for a high-tech magazine that had set up a satellite newsroom for staff writers and editors. We were covering large, annual wireless trade shows in San Diego and Los Angeles. Later that day, we learned that some of the people coming to the shows had died on the doomed 9/11 flights.

The day’s devastating events had distracted me, and–like everyone else–I felt an urgent need to be with my loved ones to digest, assess and mourn the national tragedy that continued to unfold. Before running out of my hotel room that morning, I had had to make do with quick, soulful calls to my husband and son, my mother, my daughter, and my best friend back in Denver. That’s where my mind was when I stopped briefly to glance at a man who had addressed me as I walked back from a business meeting.

“Can you spare some change?” he asked as I approached West Market Street in San Diego’s beautiful, historic Gaslamp Quarter.

With his stringy ponytail and scraggly beard, he looked like a throwback to the 1960s. He wore a worn baseball cap, a white camp shirt rolled to his elbows and gray chinos. An old, orange backpack, the kind with a drawstring, slouched down his back.

I was lugging a laptop and a briefcase, and was wearing a business suit and high heels that were killing my feet. Otherwise, my hair, jewelry and makeup were immaculate. I looked like a professional woman walking along a busy city street on one of the worst days in our nation’s history.

“Sorry,” I told the seemingly harmless panhandler in clear, unaccented American English, “I don’t have any change.”

I shrugged and smiled apologetically. It was the quick reflex of a woman who felt bad that she could not help someone in need. As I turned to cross the street, I heard the panhandler say to me, as clear as a bell, “Fucking spic. Go back to Mexico.”

His cavalier tone took my breath away. It was the first time in my life anyone had ever used hate speech like that in my presence.

His words stung, but more than anything, they confused me. What had I said or done to warrant such treatment? What outward signs or subtle inferences had he read in my body language or demeanor to lead to such a hateful diatribe?

My family roots run deep in the United States. Seven generations of my family have lived in Colorado alone. On my mother’s side, we can trace our history back to the early 1700s in Spanish colonial New Mexico.

Without knowing much about the panhandler, my instincts told me that my mestizo family had lived in the continental United States as long, if not much longer, than his. What about me made him think I was an immigrant from Mexico?

What about me made him feel superior, and within his rights as a human being to aim such ugly words my way?

What does the puerile “spic” mean anyway, and why does it bother me so much?

And, more importantly, even if I were an immigrant, did I deserve to be treated that way?

Maybe he was just a crazy old dude who was desperate for money so he could buy some smokes, some booze or some other form of self medication. Maybe he needed the money to buy his next hot meal. I’ll never know. I can try to rationalize the stranger’s behavior all I want, but that incident will always haunt me as an ugly afterthought every time I remember 9/11 and the shock, grief and sadness that followed that day.

Not long ago, this distasteful memory intruded my thoughts again when I watched a YouTube video of a British woman who unloaded an arsenal of F-bombs and racial epithets on a crowd of unsuspecting fellow passengers who were riding a public tram home after a long day of work in London.

The woman’s twisted, tired face, her unflinching and unapologetic cursing, and her unveiled anger and hatred were bad enough.

However, what really made the video shocking for me as a mother was the juxtaposition of her smallness, of her base fears and racism set against the innocence and beauty of the small, blond boy who sat quietly in her lap during her tirade.

The lad, of course, was her son, and he clutched a small houndstooth cap and a plastic action hero as his mother sank into her heart of darkness. Even if he had wanted him to, the boy’s toy could not save the day for him or his mother.

A vigilante videographer who was riding the tram that day captured the entire, sordid event, and uploaded it to YouTube for all the world to see. Before the vigilante removed the video, it had received nearly 13 million hits, and has since inspired countless video responses, farcical remixes and the predictable, low-brow ramblings of bigots hidden behind their online handles.

Police later arrested the woman, and held her for ethnic intimidation, and for being a public nuisance, a move that drew criticism from free-speech advocates.

For me, though, the image of an angry mother and a quiet son conveyed more than any of the foul language hurled by the panhandler or the tram lady. What we saw in that video was the changing of the guard, the passing of hatred from one generation to the next, from parent to child, from church to disciples, from candidates to voters, and from radical religious and military leaders to brainwashed followers.

I can’t tell you exactly what incited the British woman into her hateful rant against immigrants. Maybe she was tired, or had just lost her job. Maybe her husband had dumped her that morning, or she had just learned that her son had leukemia. Maybe an immigrant had crossed her in some way, large or small, on purpose or by accident. I don’t know, but I don’t have much sympathy for her.

Like the rest of us, she is another traveler on this planet we call Earth. We are all victims of the geopolitical system and the unprecedented financial and political upheaval around the world that is spurring new human diasporas centuries after the sun finally set on the British and other European empires.

Even here in Denver, an historically insular “cow town” adrift in a vast sea of land on the massive North American continent, we are receiving newcomers.

Progress has marched into the Rocky Mountain West, clogging our highways, crowding our supermarkets, and polluting our air.

In-migrants from California, Arizona, Texas and back East are flocking to our higher ground to get away from even denser traffic, bigger crowds, and filthier pollution. Immigrants from India, Russia, Africa, Great Britain and, yes, from neighboring Mexico and the rest of Latin America, are arriving in greater numbers every day.

All around Denver, they can be felt: Russians operate amusement park rides and sell hotdogs on the 16th Street Mall; African cabbies smoke and talk outside the historic Brown Palace Hotel as they wait for customers; Indians run our IT departments; and the latest wave of Mexicans (because they have been here all along) cook our food, build our homes, pick our produce, tend to our lawns and clean our hotels.

Recently, an immigrant from Barcelona, Spain, trimmed my son’s hair into a faux hawk, and lisped her country’s name to a boy enthralled by pretty women with accents.

More and more Brits are coming to Colorado, too. I’ve encountered them in hospitals and in my own suburban neighborhood, where they sell real estate, and their children play soccer on the same “football pitches” my son played on. Because of their charming accents and their European heritage, they are embraced by Americans with open arms. English is their native language, so it’s not difficult for them to adapt.

They blend in. They assimilate. They thrive. Their children speak English with uncanny American accents, except when they are asked to imitate Harry Potter on command. They eschew the Old World traditions their parents lug around with them: bangers and mash, heated teapots, Christmas pudding, and minding the gap. They like fitting in. They like their new world. They like being American.

This year we marked the 10th anniversary of 9/11, and we honored those who died under harrowing circumstances or while displaying unimaginable heroism while trapped in stairwells and on those doomed flights. Secretly, and in public, we lauded those who captured the terrorists, and many of us vowed never to forget the fanaticism and hatred that caused so much death and destruction.

Yet, all it takes is one angry voice to bring it all back.

My deepest hope is that the tram lady’s son will grow up to find his own voice, and that it will be one that inspires love, acceptance and peace.