and give his information to Scientology/Seventh Day/Mormons, subscribe him to all the weird mail crap you can find, send him a glitter package (https://shipyourenemiesglitter.com/), and leave a bag of flaming poo on his doorstep.

Or just chock it up as a loss and never deal with him again.

BTW, if you need to stop a gas leak temporarily, wrap the junction with self-sealing silicone tape. It's miraculous stuff for about $6 a roll.