I too have been in similar situations. My mom never kept a guy for very long.. and the ones that she did have around were total fucking losers. One of them pissed me off once, so I went outside on the back porch, where he had a case of beer sitting... and I took a sledgehammer to every last one of them. Well, except the one he was already drinking. I took it and dipped it into the open sewage drain out back and sat it back on the porch. LOL... talk about a bitter beer face.

Anyhow, if the fucker likes acid so much, why don't you just offer him a drink or something and drop several hits (enough to turn him into a vegetable) in it?
Just a suggestion.

Or you could just call the cops on them like everyone else said.