Show up for the interview and nobody is ready to talk to you. You sit for a half hour or whatever waiting for someone to come and then it's just some HR guy and you just sit in his office for an hour.
You're dumped in a conference room with a programmer to interview you and he has no idea who you are or what to ask you. Or he's ridiculously junior and has no clue of how to qualify you. They obviously haven't read your resume before the meeting and have not prepared for you at all.
They schedule phone interviews and then don't call, or are just like a nightmare to schedule, like "can you do it at 8 AM ? no? well how about 7 PM? " . Or the ridiculously no-notice scheduling, like "I have a spot in 10 minutes can I call you then?". WTF give me a range of reasonable hours I can pick from let's not send specific times back and forth forever.
They fly you somewhere for an interview then give you minimal or shitty help finding hotel/transportation etc. That should be all completely mapped out for you so you feel taken care of. They make you pay for expenses and require receipts for reimbursements, and don't pay for weeks or unless you bug them. Relic did that to me and I don't think I ever got reimbursed.
Interviewing was one of the things Oddworld did really well. It doesn't take any more time or money to do it professionally and it creates such a better impression that you don't have your head up your ass.
The other thing I see even from pretty smart programmers is asking questions that are totally opinion/style questions and acting as if their way is the One True Way and anyone who doesn't get it is not a great candidate. They might for example ask you do write a class factory and if you don't use a Meyers style "Singleton" pattern they think you "don't get it". Not only is that dumb, it's just a horrible way to qualify people because it isn't testing anything except whether they agree with your style choices.