I'm gonna say Mankind and Chainsaw Charlie vs the New Age Outlaws on Raw. The outlaws put them in a dumpster and pushed it off the stage after beating the shit out of Foley and Funk for quite a few minutes. It was truly hard to watch at the time. I was young so that might have been part of it, but still.
More recently Bob Holly cutting his back on the (?) table it sliced him from one side of his back to the other.. it made me a little light headed.
And when Mercury got caught in the face with the ladder during the TLC (mighta been a ladder match) match. That shit was fucked up.