Why did "Slim" . . . . .

As we all (should) know, one way of flirting is to playfully insult a person of interest. I think it's supposed to spark some thought, catch someone a little off guard, and see how they react to a little tease. A smart and confident person will give an appropriate response, while a dope with a short fuse would out him/herself.
Problem is, it can backfire. I once worded something poorly to a woman I really loved (and always thought was out of my league), and things were never the same. I begged her to understand I was only joking, but she was hurt. After that, we'd say hi to each other in passing, but I never felt comfortable with her again.