1. Keep and renew the domain name; it's too cheap to even be concerned about
2. What negative response? Are you selling stuff and making a profit? That's all that counts
3. If not, why not? Sometimes a provocative name like that is an asset (it's how "Big Ass Fans" got started)
4. Look at your referral traffic in the server logs, see if you can spot any common keywords that you could build into a different domain name to try out (although I don't think you could go wrong with "undies" and I assume they are men's without going to your site)
5. If not running AdWords campaigns, go ahead and buy some traffic for highly targeted keywords in [exact match] only; make sure you've got conversion tracking for sales revenues in place or you won't know what you earned from what you spent; make sure you break even on sales at least, otherwise you have a serious problem
6. If already doing AdWords without success, get your campaigns audited to see where you're going wrong (everyone does)

My book on Amazon could help you ("The AdWords Bible for eCommerce") with 5 & 6

All the best!