Sheldon Cooper wouldn't be caught dead wearing those.
I have a soft-spot for Sheldon. He, like me, is an asexual from Texas.
In the pilot episode, Sheldon got "pantsed" and we got to see the off-white briefs he was wearing. So, this is consistent with your premise.
However.
We know, since he said it clearly in the show, that Howard wears Aquaman briefs. And, bear in mind, the scene where Penny finds the Spiderman undies, which she "assumes are Sheldon's," to which Leonard responds "it's so hard to find them in his size."
I get the distinct impression that the characters in that show might surprise you with their choices.
