If your date arrives more than ten minutes late more than once, there's a pattern there. He's saying "I don't want to get into this."
Rudeness to waiters
Or taxi drivers, or anyone else in service jobs.
Divorce horror stories
Your date launches into the story of his messy divorce and how it was all his ex's fault. Anyone who's emotionally grounded knows it takes two to contribute to a breakup.
Say you're on a date with a new guy. You mention that your last relationship lasted a year and he says, "That's impressive!" When a man over 30 tells you all his relationships have ended after a few months, that's a red flag.
All kids have issues and some may not like Dad's new girlfriend. But if they're spoiled brats or excessively angry, head for the door.
If a man suggests splitting the tab on a first date (no matter who asked who or what each of your financial status), that's a red flag.
You might want to think twice if a guy tells you none of his previous girlfriends was good enough for his mother.
It may get better after a first awkward time, but bad sex two or three times in a row will only get worse.
Dirty under things is the hallmark of a secret slob and secret slobs have many worse habits you don't even want to think about.
The anger hum
As your new guys talks about past lovers, work, friends, family, etc., listen for a low hum of anger. Everyone has a bit of a temper, but recognize deep-seated anger and back off when you sniff it.