It's a toss-up between:
Dark Forces, mucking around with claymores and dropping them repeatedly at my feet with the motion sensor on. First one explodes, I launch up, fall down, hit the ground just before the second blows. Fly high enough into the air that the fall damage is fatal.
Castlevania: Dawn of Sorrow, fighting a Final Guard. He raises his shield, I'm too close, so the bottom edge smacks me, dealing damage and knocking me FORWARD. Not back, as in "knock back", but forward, i.e. like it hit me in the back and not the front. I end up in his sprite, take another buttload of damage from the contact and get knocked back to where I was. Lather, rinse in blood, repeat until dead.