Yeah, that might be a bad idea. It may come back to bite you, if you know what I mean. Usually after a break-up, friends are pretty much off limits. Not general mutual friends... but definitely "best friends" of the ex.

It puts the friend in a predicament. If he tells you no, does he tell his best friend that you called him? And if he doesnt, will he feel funny about keeping it from him?

And if he says yes, does he tell his best friend that he went to the show with you? If he doesnt, and the ex finds out - it makes you both look guilty. If he does tell him, he runs the risk of losing a best friend out of the deal (just out of "guy pride").

So for everyone's sake, I'd say yeah - that might be a bad idea.