Thank you all for your various responses. Perhaps I should have been more clear about my question.
First, I was not asking for a poll on whether sleepovers are still socially acceptable after the age of 20. Many of you have advised that I should not go because sleepovers are immature, cheesy, and a waste of time for grown adults (a perfect example being Young Thinker’s sarcastic response, “How cute! However, even if it is perfectly innocent, a coed. sleepover still doesn’t quite “look right!””). While I respect your social standards, this simply was not the question I was asking. I was asking how likely it would be for a sin to be committed if I went on the sleepover.
Second, I should clarify that, based on my knowledge of the type of people that will be at the sleepover and the type of atmosphere to expect, I am fully confident that there will be no sex or inappropriate contact, and very little drinking. (If my expectations turn out to be wrong, I am planning to leave promptly.) Many of you have advised that I should not go because the purpose of most sleepovers is to have sex (the perfect example being TheRealJuliane’s surmisement, “I mean, seriously, what group of 20 somethings gets together for a “sleepover?” You KNOW the end game is sex!” Others of you pointed out very nicely in response that sleepovers that do not end in sex are in fact very common. My “prudential judgment” for this particular sleepover is that I won’t have to worry about sex or inappropriate contact taking place (and again, if I am wrong, I will leave).
With this being said, since I am not concerned about sex and heavy drinking on this sleepover, I want to clarify the type of sin that I am concerned about. I am wondering whether guys are more prone to lustful desires during (“innocent”) co-ed sleepovers. I am worried that, even though there will be no sex, some guys will be more likely to consent to impure thoughts and desires because of the girls there. I am willing to make the sacrifice and not go in order to decrease the chances of a sin being committed; but I feel like maybe I am being overscrupulous, and maybe I should just go, and trust that the guys are mature and respectable enough not to succumb to such thoughts.