If you don't look at the trade in hindsight, one of the worst was trading three picks in the 1979 draft (#3, #9, and #21) for Bob McAdoo. Bill Cartwright, Sidney Moncrief, Vinnie Johnson, and Cliff Robinson were some of the decent guys who came out of that draft.
Of course, that one turned out okay, because we traded McAdoo for another pick, which turned out to be #1 overall, which we then in turn traded for McHale and Parish. Still, in terms of value, McAdoo wasn't worth nearly what the team gave up.