This one'll be quick.
I was watching "The Producers" (the real one, not the musical) on TCM the other day; it'd been awhile since I'd seen it all the way thru and thus awhile since I'd seen Dick Shawn as "L.S.D.", especially his performance during the "performance" of "Springtime for Hitler".
It just took a few moments until I found myself thinking, "So this is where Robin Williams got his shtick".
Go watch it and tell me I'm wrong.