There was a fellow we tolerated for a while before we decided he just wasn't a very good match for the group.
Let's see about highlights.
* In a D&D game, after a bad encounter, we all decide to flee. He's in the back (he's a wizard), so he casts Rock to Mud in our path so that the monsters will eat us so he can get away. At the time we thought it was funny (a lot of our D&D games are pretty "beer and pretzels" dungeon crawls without much roleplaying anyway) so we didn't think much of it.
* The players are hired by a patron to deal with a local Ine Givar cell. I get a note (really a message on my cellphone) saying he goes and meets with Ine Givar cell in question to see how much they'd pay him for information on what the other players are doing. They offer him 1 million credits. He accepts, and lets the Ine Givar track them. This obviously led the players to fail and one of the players to be blown up by a bomb left in his room. (Obviously, the Ine Givar didn't have a million credits to pay, so they didn't).
* There was another game where the players came upon a "mercenary camp." The players were pretty sure it was actually Sword Worlders with some Zhodani advisors (the game was in the run-up to the 5th FW) about to do some sort of mischief. The player thought it was a bad idea. The party wanted to approach using some likely excuse (we were traveling under the guise of being a few big game hunters along with their guides/assistants/assorted hangers-on aboard the Safari Ship
The Mutual of Oriflamme). The party overruled him but the party told him he could go back to the ship if scared. He does so. But then he passes me a note that says "I slash the tires of the party's vehicles on my way so they can't get away." So much for an ex-Imperial Marine 5 terms with a SEH. When negotiations start going well (the party had a slick talker) he asks me if he can hack the gunnery system to fire the missile launcher at the camp. I let him hack the computer (he has computer skill) but then tell him as he has no ship's gunnery skills he has no idea how to repurpose the missiles intended to hit starships in space for ground targeting to which he says I'm just nitpicking and that it should be easy.
* It was basically normal for him to do things like promise to other people that another (wealthier) player would pay some debt. For instance, the group goes shopping for equipment. He buys a Air/Raft, a hostile environment suit, and a bunch of other equipment. His character at the time had a reasonable sum of money, so I didn't think anything of it. Later in the game, he goes to a casino and tries to bet 100 000 Cr on something. I ask him where he has the money because he shouldn't have that kind of money left after buying all that earlier equipment. He claims that the noble character in our party (who was rich) paid for it all. The noble player replies, "This is the first time I heard about that." Then: "Oh, then I'd have just found his bank account number while we were on ship and taken the money to pay for it."
* Eventually he played the Scout who got a Scout ship mustering out and he said he'd be the transportation for the group. Of course, anything, literally anything involved the line "what's in it for me?" and that the rest of the party should pay him (not just cover costs) for use of his ship. Then he'd want to also come along on any jobs and assumed he'd get an equal portion of the pay.
Those are the incidents that come to mind. I think that if it was just one character that acted like this, it'd be annoying but perhaps memorable and nothing would have come of it. That it was something he did across all of his characters despite talkings to and so on made him eventually a persona non grata.