Diogenes of Sinope (412/404-323BCE), or “Diogenes the Dog,” was guided by his philosophical views (he was a Cynic) to live in a tub in the marketplace, in an attempt to live as close to nature as dogs do. He frequently ridiculed public figures:
while Diogenes was relaxing in the sunlight in the morning, Alexander, thrilled to meet the famous philosopher, asked if there was any favour he might do for him. Diogenes replied, “Yes, stand out of my sunlight”. Alexander then declared, “If I were not Alexander, then I should wish to be Diogenes.”
Diogenes was also fond of making his point through obscene demonstrations:
Diogenes is said to have eaten in the marketplace, urinated on some people who insulted him, defecated in the theatre, masturbated in public, and pointed at people with his middle finger. From “Life of Diogenes”: “Someone took him [Diogenes] into a magnificent house and warned him not to spit, whereupon, having cleared his throat, he spat into the man’s face, being unable, he said, to find a meaner receptacle.”
He often accused Plato of vanity and conceit.
Plato had defined Man as an animal, biped and featherless, and was applauded. Diogenes plucked a fowl and brought it into the lecture-room with the words, “Here is Plato’s man.”
Sources: Wikipedia, Lives of Eminent Philosophers (Diogenes Laërtius)