I've gone before, most of the guys will be in tighty-whiteys, some (at best 1/4er) might be in jockstraps, but it's mostly boring. One guy i was talking to pulled down on mine to look at my junk without asking needless to say, since I wasn't being paid while there, I stopped talking to them after saying "what are you doing?" and they said "I thought you were one of the strippers".
For protocol, be sure to get consent before trying anything. Socks and armbands/guards are great for putting money/cards/phones. At that same party some old guy pissed on another participant without asking which is so very, incredibly, uncool.
like most parties, be a decent human being and you should be fine. don't be afraid to tell the staff if anyone is being aggressive/abusive. It helps everyone there if you do and they're liable if anything bad happens.