What's your "litmus test" to decide not to date a person twice?

I had a date with a girl once that ended with her dad pointing a very large handgun at my head. I didn’t offer her a second chance…

Sorry about that Jamshid. I tend to over-react sometimes. But you really should have had my daughter here on time.

If they say no when I ask. So far that is the only way.
Either I’m not fussy enough, or just desperate, or both.

How about this one?

Years ago, as a little sophomore, I was asked out by a graduate student. He asked me to his apartment and showed me his gun–a rifle or shotgun! I think this rates as a reason not to date someone twice:)