When two men have so much sex that the receiving partners cheeks get stuck together from the dried man juice like two piece of metal that have been welded. Also a manufacturing term.
Guy: Last night I was with Brian and I Butt Welded him.
Other Person: What is that?
Guy: I came really hard and after I pulled out, he didn't wash his cheeks properly so the next morning his butt crack was stuck shut.
Other Person: I am your Grandmother, why would you tell me about Butt Welding?
The act of ejaculating in your partners ass crack, and giving the cheeks an almighty clap together to seal the deal.
"Having a dirty one with the missus and the full time celebrations may have got out of hand when I went and gave her the butt weld."
When you can't get your I.D. out of your wallet from sitting on it too much.
When the doorman at the club asked Billy for his I.D., Billy had to give him his wallet because he had butt welded it in there.
Refers to metal-fabrication dat you are able to perform with just your own fart-gases due to their being so super-hot dat you can actually use them like a welding-torch.
I made da mistake of sitting on a stack of several nested chairs while chowing down on extra-spicy baked beans, cabbage stew, and hot wings at my buddy's backyard barbeque, and after some uproarious whizzpopping adventures, I ended up butt-welding da chairs together into one solid mass of metal tubing!
A sex act involving a man and partner, in which the man, with expert precision, ejaculates between their partner's ass cheeks and presses them shut, allowing the semen to dry. The dry semen forms cement, welding the cheeks shut.
"Man, that bitch Randy was such an ass until I gave him a vertical butt weld. His dumbass won't ever shit or call me gay again."