He's a bit of an internet nerd hero these days but there are some great stories about Diogenes, the Alexander the Great one is hilarious. He was sunbathing when Alexander the Great met him, and Alexander asked him if he wanted anything at all from the most powerful man in the world - and Diogenes said "yes, to move out of the sun." Then when Alexander was leaving he said "if I had not been born Alexander, I would certainly hope to be Diogenes" and Diogenes said "I as well."

The most famous one is definitely the time that Aristotle was trying to define a man and came up with "featherless biped" so the next day Diogenes showed up with a plucked chicken and let it loose in the forum and said "behold, a man!" So Aristotle changed it to "featherless biped with broad, flat nails."