How do I deal with my hyperfixating joke player?

Hey all. When I started my campaign I had everyone else make very good characters. Good backgrounds, good potential for growth, etc. it took several days of going back and forth with this one player, who I’ll call Larry, to reach something that even worked as a character.

His first idea was someone with a legendary item (nuclear bomb) implanted in their head that would detonate when they died, and he proceeded to tell me he wanted to die early on so he could play this character’s wife. I obviously immediately vetoed this.

My standards must have been lowered or something because now he’s playing a drug addict warlock whose patron is the boss of his drug company. And their name is a damn pun on LSD. I do not know how I managed to allow this. My bad.

So I establish a cartel. I establish in our third session that this cartel is bad with an encounter that results in 1200 people dying due to the party’s failure in disabling explosives the cartel placed. Now I’ve resolved this issue partly as they want no involvement with them, but for the past 8 sessions haven’t done anything to separate themselves.

All of this is to say that two sessions ago he decided his character should be very into dinosaurs. He got me to agree that he has an old dinosaur bone he got from his mother (they do not exist in this world, the big campaign twist is they are inside a bag of holding). He got it before his mother was taken away by, you guessed it, drug cartel. Now he has a dinosaur familiar that he just had to have, and one homebrewed pteranodon stat block and a lot of headaches later (he texts me every other day trying to find a loophole where he can fly with it) he wants to totally change his subclass into one that lets him do more with his familiar, and he wants me to get rid of any work I’ve done to turn it into what is functionally an imp.

This character has never shown interest in dinosaurs until about one in-game day ago.

Please send help. He is wasting everyone else’s time when he doesn’t focus on the main plot.

tl;dr my players running a joke character drug addict who’s into dinosaurs and I’m beginning to lose it