Actually, I do wear underwear, but an interesting term exists which is employed concerning those who do not. They call it to go "commando" as in "I didn't have any clean underwear Friday night so I had to go commando to the party at Jen's house."
Last year when I was an intern, I did a rotation on the urology service at the VA hospital. One day in clinic we had a 60-something year old patient return for a post-operative visit after having undergone a circumcision about one month before. He stated that his penis was hurting and wondered if there was anything that could be done about it. (You can see where this is going.) So I asked him to drop 'em, as it were, and so he dropped his jeans and I was truly shocked to see that he was without underwear, i.e. he was going "commando." Naturally our advice to him, which he seemed truly surprised by but receptive to nonetheless, was to start wearing some underwear!.
