Is it something in particular that they say or do, that really gets you. Maybe make you think, "Oh I might want to take her out again, I like her" or him, whatever the case may be.
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I am pretty easy :-) - meaning unless you disqualify yourself majorly, by default you'd get a 2nd date. The disqualifying factors like bad breath or dirty hair or hands - although I've sometimes made exceptions if the rest of the person were great.
Utter boredom is another disqualifying factor, like the person has nothing good to say - nothing I care about, nothing I don't already know, no intelligent opinion about the stuff that I say.
I used to not go on a 2nd date when there was no chemistry both ways, but on two occasions I've had dates with girls I liked who were very lukewarm towards me through the whole date (and that's being kind - I was surprised they had even gone out with me), but for whatever reason on a second date they were much more into me, and from early on in the 2nd date - which I found weird. Both cases lead to meaningful relationships so if there's no "immediate chemistry" life taught me, take it easy my man, go on a 2nd date, see what happens - girls are fickle and they change their mind.
If a person is nasty to others like they give the waiter / chef major hard time about the food with no good reason (esp. given they are on a first date with someone) that is probably the only situation in which I would not have gone on a 2nd date even with a supermodel. I despise people who are nasty to someone they sort of have control or power over, like a waiter in a restaurant.1