if you don't like'em don't wear'em.
if ya willing to wear'em to make her happy.. strictly rock them bloomer for her.
gender flip the gift exchange.
some boyfriend gifts terribly uncomfortable * physically or taste-level wise* underpants to his ladyfriend. she's under no obligation to wear said bloomers. and there shouldn't be any implication of possible infidelity at a person's reluctance to feel silly or unattractive.
you is a grown ass man. ya have earned the right to self-selected underpants! :biggrin1:
they is your loins, ensconce them as you choose.
other than standard gift receiving etiquette, ya thank you/no.. really, you shouldn't have *minus obvious attitude*, ya not obligated to suffer the indignity of unwieldy undergarments.
eta: i buy my boy underpants. i try to keep my selections aligned with what he's already got in his top drawer.
he's pretty open minded about what he'll wear for his appreciative audience, but i don't expect him to rock a jockstrap to work just because i happen to like the view.