This could be the ideal game for one of those swelteringly hot days when it's natural not to be wearing very much at a party. The game entails the asking and answering of intimate questions, and the object is to distinguish between who is telling the truth and who is fobbing you off with outrageous lies. But, as you'll discover, there's rather a lot riding on you guessing correctly.
The guys in the group will be playing against the girls, and one side must agree to reveal some of their deepest, innermost secrets – while the other side will run the risk of revealing themselves in a rather more literal way. For the purposes of this explanation I'm assuming the guys will be asking the questions and the girls will be answering them. Because it is this way round, the boys should be clad in towels (it's an open question whether they'll be wearing anything underneath, but I'll return to this later). For them, the aim of the game is to keep those towels on – and the aim of the girls is to thwart them in that quest. Simple as that.
The boys should each write their name on a separate piece of paper, and fold it twice so the name cannot be deciphered. It's important that everyone folds their sheet in roughly identical fashion. The sheets should then be rounded up and placed in a pile. Then, take some more pieces of paper (enough to make the overall number equal to exactly double that of the number of girls in the group), write the work 'blank' on each of them, fold them up and add them to the pile.
The papers should then be thoroughly mixed up so no-one has any idea which one is where, and each girl should pick out two sheets at random. She should unfold them without showing anyone else, and then read what's there. Whichever girl has ended up with a particular boy's name will become his designated 'enemy' for the duration of the game, and the one who will be aiming to relieve him of his towel at the conclusion – but, at least to begin with, he'll have absolutely no way of knowing where the danger lies. The only clue will come from the fact that she'll be required to tell him an outright lie every time he asks her a question, while all the other girls will be required to tell him the truth as far as they can. If any girl ends up with two pieces of paper with the word 'blank' written on them, she'll be the enemy of no-one, and must tell the truth at all times.
The boys then take turns in asking each of the girls an intimate question. It must be one he could have no prior knowledge of the truthful answer to. He must try and judge which of the girls is lying to him, looking for crucial clues such as non-verbal signals, the length of time it takes to formulate an answer, and of course the general plausibility of the response. Possible questions could include "who or what were you thinking about the last time you masturbated – describe in detail", "have you ever spied on someone naked without them knowing, and if so who was it?" or "have you ever – for any reason – thought about any of the people in this room when you were making love to someone else, and what was the thought?".
Once all of the boys have had the chance to ask each of the girls a question, it's time for a second full round of interrogation. The boys can use any clues they may have picked up so far to help them frame their second question in the most effective way. If, for instance, one of the girls stood out as a particularly lousy liar, it might be sufficient to ask her "that story you told me earlier about the nun and the pogo-stick – that wasn't entirely true, was it?" And if she bursts into a fit of helpless giggles at that point, you may well conclude you've nailed your enemy. On the other hand, if the identity of your opponent is still a complete mystery, it might be an idea to throw in a curveball by asking the girls questions that touch on their self-identity, values and individual sense of morality. If a particular girl has a self-image of being very giving, it will require something of a mental flip to describe herself as an inwardly very self-centred person. Requesting that she describe the nature of her selfishness in detail may well lead to her giving the game away.