I wasn't part of this RP, but I once read an very casual RP about Warrior Cats where the kids writing it kept making what I am pretty sure was accidental innuendo. It was so bad I showed it around to people IRL. I wish I had kept the link.

That I've been in... there was one time where sex scenes became in vogue in an RP I was part of. One guy, trying to keep up with the trend, wrote a sex scene where he described a blowjobs looking like... I think the word was "Headbutting"?