PARIS Hilton plaything Stavros Niarchos III is some kind of class act. After he fueled up at L.A.'s Element club the other night, the Greek shipping heir and a posse of pals stopped at Burger King. "Stavros offered a homeless man outside $100 to dump a soda on himself," a source squealed to Us Weekly. The desperate bum took the payout "and everyone laughed," reports the source. This one's a keeper, Paris!