I'm going to vote for someone who turned out to possibly be the Bills worst draft pick ever, Tom Cousineau. Check out the names here (wikipedia):
Cousineau was selected first overall in the 1979 NFL Draft by the Buffalo Bills, who acquired the pick as a part of a package of five draft picks from the San Francisco 49ers in a 1978 trade for O. J. Simpson. However, he never played a game for the Bills. He instead signed with the Canadian Football League's Montreal Alouettes, who signed him for double the money originally offered by the Bills. Cousineau became a star for the Alouettes, becoming the Grey Cup Most Valuable Player in the 1979 season. He only played in four games in his third season because of an elbow injury while the Alouettes collapsed.
In 1982, Cousineau wanted to return to the NFL, choosing to forego two optional years with the Alouettes. The Houston Oilers attempted to sign him, but the Bills (who still held Cousineau's NFL rights) matched the offer. Cleveland Browns owner Art Modell had long been interested in signing him. As a result, Cousineau was traded from the Bills to the Cleveland Browns for a first-round draft choice (14th overall) in the 1983 NFL draft, plus a second and a third draft choice in subsequent years. That first-round pick was used on future Hall of Fame quarterback Jim Kelly.
Due to his disappointing NFL career, Cousineau is considered to be a draft bust.