n. def. 1. the ex-girlfriend or boyfriend of one's friend. 2. former, repeat hook-up of said friend. 3. said friend's long-term crush?

XX: So you want to date your friend's former flame. If so, does it matter how they broke up or how the crush ended?

XY: Yeah it definitely matters. If the ex was a cheater or dumped your friend brutally, it's a lot worse than, say, if your friend tired of having a girlfriend. However, before we talk about degrees of acceptability, I think we need to settle whether the ex is off-limits entirely. I can see the argument that he or she is.

XX: For the first month after the breakup, I think it's pretty reasonable to keep one's distance. There are matters of propriety to consider. You don't want to be a Claudius marrying your brother's widow mere weeks after the fact.

XY: Wow. A month? I agree with you that there is some sort of reverse statute of limitations, but while you advise our readers not to prosecute that ass for at least a month, I say play it safe. If my friend started going out with my ex a month after the break-up, I'd be very suspicious of this vulture. Was he advising me to dump her because he wanted my leftovers (or sloppy seconds)?

XX: A month seems brief if it was a real relationship, but if they just hooked up a bunch of times and you and the ex have real chemistry ... I'd like to propose a calculation whereby the longer the couple lasted, and the better the friend, the longer before you can tap that ass (or eat the leftovers).

XY: Come on, though. Aren't there exes who are just out of bounds?

XX: A best friend's ex is almost always taboo, but in matters of the heart (and not just the bed), I don't make steadfast rules.

XY: I don't make 'em, either; I just live by 'em. Actually, I live by the Code. The Code is unwritten, but any decent guy knows and abides by its regulations. Besides, unless your buddy has absolutely no feelings towards his ex (doesn't hate her; doesn't love her; doesn't remember her, preferably), just as friends don't let friends drive drunk, friends don't pork their buddies' exes.

XX: I like that. But what about your buddy's crush? Do you pork her?

XY: With a crush, you're treading dangerous territory. Asking him can work, but I wouldn't expect him to tell you what he actually thinks, lest he appears immature and possessive (of a girl he's never even dated). He may in fact be the most sensitive of our three ex examples.

XX: Still, just because my friend liked some guy but never had the guts to make a move, doesn't mean I can't date him, especially if he shows interest and I think it could go somewhere-

XY: -oh, I agree with you. In principle. The crusher has no stake in the matter. Just don't expect her to see it that way.

XX: So avoid ex-crushes, unless you'd be willing to take a risk, mess things up with a friend, then not even get the guy or girl in the end. If I were an econ major (or maybe I am), I'd tell you to do a cost-benefit analysis, maybe even make up some graphs on Excel.

XY: Cost-benefit analyses won't get you anywhere. Unlike an econ problem set, you can't arbitrarily assign a value to a lifelong (or college-long) friendship, and then weigh it against the arbitrary value you assigned to the utility you'd derive from a relationship with his ex. Nor, for that matter, can you with any accuracy forecast the probability of things working out.

XX: If you have to think about it, it's probably not a good idea. It's Amherst: There's another one out there. And he's just like him.