A weird thing that I have noticed (because I'm apparently kind of a perv)
Two of my OTPs are Clex and Kirk/Spock, which you may have noticed are both guy on guy, where one of the guys is an alien/half-alien. One of the great things that fanfic writers have noticed (a lot of noticing going on here) is that when writing hot sweaty man sex where one of the men is an alien(/half-alien. Whatever) is that the alien can be self-lubricating for ease of sexing each other up. Here's the weird thing: the overwhelming majority of these that I have seen have Spock lube up his penis, while Clark lubes up his... back door. Weird.