They tell you that everyone they knew before you abused them or rejected them. They have a very black-and-white sort of attitude about people and about life in general. People are either good or bad, no in-between, have treated them poorly (everyone in the past) or treated them well (you, while you're still in favour). When you're with them, you feel anxious and stressed after the initial charm and excitement of the friendship wears off.

Good grief, I wish I could give past-me a good shake!

Thank you for posting this. It's all spot on, but most especially the last point. Ah well - once bitten, several times shy...