Jim Kelly -- legend -- does what he wants, when he wants ... and that includes drinking your beer.
The Buffalo Bills legend was signing autographs at the Pro Football Hall of Fame in Canton, Ohio over the weekend when he got thirsty.
Kelly saw a fan with an ice-cold beer mug and decided to make his move. The fan tells TMZ Sports he was stoked about the encounter and happy to help out.
Fun Fact: The beer and mug combo ran about $10 ... by our count, Kelly owes the guy $3.