When you take a chance in a relationship that's moving too fast, and realise taking that chance was a bad idea. You then quit the relationship, by chancing out.
Person 1: I've been dating Joe for a week, I don't really know him.
Person 2: You really took a chance with him.
Person 1: Yep. Bad idea. I'm just going to chance out.
To cop out of a relationship when you have been dating for a very short period of time; or just end the relationship when you know you shouldn't. Ususally when you don't know the person very well.
Person 1: So Robbie and I have been dating for a week now, but it's not really working out...
Person 2: Are you gonna chance out?
Person 1: I'm thinking about it.