Worst pitch in modern Red Sox history. The official scorer called it a wild pitch, because it almost hit Wilson... and how history could've changed if it did.
There are plenty of contenders for worst nightmare: the Leephus to Tony Perez in '75 that tied Game Seven (Yaz called it "that slop curveball by Bill Lee"); Torrez' meatball to Dent; maybe Wakefield's floater to Boone or something by Pedro -- (probably the one Matsui ripped after the mound conference; Posada tied it with a pop-up)... but both those guys are thought of as heroic for their efforts.
Stanley's to the backstop had to be the biggest letdown, one out away from a world title. That was worse for me than Buckner's E, because once NY tied it -- and the way they tied it -- we all knew the outcome was inevitable. But I remember my step-father, who was a catcher and a Mets fan, just saying, "That had to be a cross-up."