During our first trip to TTR, I tried to wear very small swim-shorts to lingerie Night, but the little guy at the door wouldn't let me enter. My wife had just gone inside wearing almost nothing -- and I wasn't about to leave her for the night -- so I literally had to just force my way past the guy at the door. He tried to stop me by grabbing my wrist, but not with much enthusiasm -- so it didn't take much to get inside. I felt bad every time I saw him for the rest of the week though. The next year I brought boxer-briefs, and had no difficulties.
Most of the guys we saw allowed to enter had boxers on with t-shirts or shirts. Amy (from the entertainment team) was on the door and guys were not allowed in if not (un)dressed for the occasion however, when the casino part had finished, guys could go in fully clothed.
