I'm always slightly weirded out when a girl casually says "my boyfriend." This is either because a) I suspect that she's giving me a not-so-subtle hint to back off, or b) I'm not a big fan of calling people by anything other than their given names. In my entire life, I think I've said the phrase "my girlfriend" twice, and I remember both times, just because it seemed so strange. "My ex-girlfriend" is even stranger, if only because there isn't anyone in my life whose defining characteristic, to me, is that she's my ex-girlfriend.