Sabotages the game, every time.
Sometimes its because he dislikes being boxed in, but he is aware my co-dm has trouble running free form. He is aware we are running via module. He still insists on crazy plans that bypass 3/4 of the adventure. We either bend over backwards for him, or let it go to shit. I stepped OOC for a moment and advised him that this derails the campaign so hard there wont be coming back, and hes fine with that. Bored from all the talking, I think.
One shot time, he literally sold his golden ticket to the adventure. It wasn't a great one shot, I wasn't very good, but it was the first I had written myself.
Instead of boarding the golden sky chariots his halfling rogue attempts to sell the ticket to a noble, forcing me to basically abduct him with a nearby paladin.
He then proceeds to murder folks for their door crasher prizes for reaching certain points on the floating island first, despite getting a bunch of his own.
The only request I had for this one shot was "make good characters" and as soon as he sees a shiny he makes with the kidney stabbing.
Shit, I could go on. Thing is, he's acknowledged its a major issue but doesn't know what to do about it. Probably doesn't care anymore. So we forge ahead and make do.
To be fair, it was less his actions and more that of another player that torpedoed this campaign.
Why wouldn't you just bail on the plan when you flubbed your intimidate check instead of trying to kidnap the uber powerful astropath with a digi melta at gunpoint?