Which of these is most likely to make you say "no second date"?

Talking about their ex or exes.

Farting loudly: If it's like, one accidental fart, then it's fine. If he's purposely blasting them, then that's another story.

Talking about themselves constantly: It's a first date. We're supposed to talk about ourselves. If he won't let me talk about myself and keeps yakking then there's a problem.

Complaining: Depends on what he's whining about.

Talking about things that are boring to you: I'm a boring person, so nothing people can say can bore me.

Looking at their phone: THIS ONE. It pretty much says he has no interest in me and that I wasted my time.

All of the things you listed are not that bad really...they could even be brought on by nervousness!

Being cheap is one that gets me. It's great to be smart with money but there's a time and a place for it. Don't haggle, don't ask for free shit, don't talk about prices. And if you asked me out, you pay! I would never go on another date with a cheapskate. That shit is ingrained, it's not some small bad habit that can be corrected.

Skydiving without a parachute

Treating strangers (e.g: waiters, bellboys, taxi drivers) like shit, monopolising the conversation (it doesn't matter if they're talking about themselves or not, conversation involves balance), looking at their phone for long enough to constantly stunt conversation, complaining about petty things and vocalising extremist political views.

All of these are pretty rude things to do on a date, except being boring. So I'd say any of them.