Robert Nelson, aka The Butterfly Man, is one of San Francisco's most prominent street performers. His routines center around juggling, object manipulation, and the fact that he is much better at insulting you than you are at heckler insulting him. I know at least two people he made cry. One because of laughing, and the other because of the insults. He is an extremely popular performer at Pier 39 (one of the best busking spots in America), and has won their performer of the year award multiple times.
He has a W.C Fields-ish persona. He keeps hitting on women and making fun of the children ("Now this is real fire, and to prove it - I'm going to burn this kid right here!"), but as time has gone by his act has become more joking-curmudgeon, rather than mean-curmudgeon.
Nevertheless, his routines are really damn funny, and if he is in a venue where there aren't any kids, they can be shockingly explicit. He was profiled in the book Passing the Hat, and it ended with the following description of his show's finale:
The ending of the show is close to Butterfly's heart, and when he squeaks, "Now, this is sensitive, so - shut up, you creeps!" he means it. Balancing a long-stemmed red rose on his nose, he recites:
It matters not
The job you've got
As long as you do it well.
Things are made by plans well-laid;
The test of time will tell.
But how can you count
Or know the amount
Or the value of a man?
By the show displayed,
Or the beauty made
By the touch of the juggler's hand.
And sweeping off his velvet cap, he bows from the waist with arms spread wide and the top of his head towards the audience to disclose the tattooed butterflies there that give him his name - and ensure that he will never return to the straight world
Some of this bio came from meeting the guy and hearing him tell stories, but other bits came from a really good book called Passing the Hat by Patricia Campbell. If you would like to learn more about street performing, that is the only book on the subject.