I have a theory that everyone has to have had at least one crazy ex in their dating history, so that when the right person comes along, they can truly appreciate them.
My crazy ex threatened suicide at one point when we were dating. I talked him out of it. (Honestly, in retrospect, I think he was doing it for attention, not out of any real intent to commit suicide.) Then, a couple of weeks later, he dumped me by IM.
My husband's crazy ex is a piece of work. She thinks I stole her boyfriend even though he dumped her a year and a half before we started dating. She was also obsessed with wanting to be in my sorority (did I mention how glad I am she's not my sister??) I've posted about her
here and elsewhere.
On another note... we never formally had a rule about asking permission before dating a sister's ex, but that's just the right thing to do - sisters before misters, and all that. One fraternity I know of did have that rule, and permission was very seldom granted - I know of a few women, including a couple of my sisters, who couldn't date someone in that fraternity because they'd dated someone else in the fraternity and the ex wouldn't give permission.