You can also defuse the situation by offering to increase the stakes, and letting the other party back down. "Let's both solve the same programming problem, and see who gets done faster. Would $500 be an interesting wager? Of course, I might use a different language if I think it would be better for the task at hand, but I win most of my competitions with Perl."
This approach does leave an impression. Make it clear that CPAN is part of Perl, and don't challenge anyone who knows Haskell.
It should work perfectly the first time! - toma