By far, Bill Buckner for me.
I was coming off such a high of the C's in 86, then was devastated by the Len Bias death that the Sox had captured me in the fall, only to be crushed by a "slow roller up the first base line". I hear that call in my sleep, still. How could Mcnamara leave Buckner in. It's why teams carry defensive specialists, to substitute when the game is on the line!