Old fans will say that the original Midnight Massacre was the worst trade in team history, I would agree, had I seen it. For newer fans, the worst trade in history is what I like to call the "New Massacre."
Scott Kazmir was a young phenom from Texas when he came to the Mets in 2002. A highly rated pitcher, he wowed people with his pitching, and seemed almost destined to be a member of the Mets soon-to-be-great rotation. Fate wouldn't have it that way, as Jim Duquette, apparently in one of his three sparks of stupidity (signing Kaz Matsui, trading away Jose Bautista), felt that it would be better to get a guy with arm problems in the rotation.
And thus, Kazmir (and Jose Diaz) were sent to Tampa Bay, then known as the Devil Rays, for Victor Zambrano, otherwise known as the "Wrong Zambrano," and Bartolome Fortunato.
Zambrano is known for being a nightmare on the mound, and not in the positive sense. Even Rick Peterson, the Oakland Athletics pitching guru brought over, couldn't help him, and he soon faded away. Fortunato made a couple appearances, but ultimately he also faded into obscurum.
As for Kazmir? Eh, not much, just two All-Star appearances, the 2007 strikeout crown and a World Series appearance, Oh, and before David Price, he was considered one of the greatest pitchers in Rays history. Yeah, not much at all.
As of now, all four are out of Major League Baseball. Kazmir, by far, is the funniest example, as he's in independent ball playing for the (snicker) Sugar Land Skeeters of the Atlantic League.