Friend, foe, or both?

One thing I never understood was how one minute people could absolutely dislike someone, telling other people how they screwed them over, go out of their way to avoid or ignore them and then suddenly start hanging out with them and being friends? It makes no sense! I have encountered this many times (usually with girls, no offense meant) and it doesn't make sense. For instance I know two girls who were at odds with each other, one not liking the other and vice versa for one reason or another and suddenly I see them going out, hanging out with each other. What the heck? When did this happen?

When did you suddenly become friends with this girl? I mean it doesn't make sense. Is it really a kiss and make up sort of thing? When did that memo go out? I mean you guys were both at odds so much before now going out and having fun. So strange. It perplexes me how they go form being so mean to being friendly. Is it an act? I mean why go through so much to like someone? Such strangeness or maybe they got over it just randomly? A mystery for our time.