I think the topic of sex is a very common subject at some point in the conversation when you get several people together, whethers it's at work or sitting with your friends around the kitchen table! There aren't laws against simply talking about sex, the laws protect people from sexual harrassment, but I think that anyone that was offended by the subject matter should just leave the conversation and not get involved! It actually can be extremely informative, funny, lighthearted and you might even learn something:)
the department in the company I worked for was all females, so we would talk about sex all the time! Anytime a guy from another department walked in on a sexual conversation he would turn red and got out of there as fast as he could!!! hahaha As long as everyone is comfortable with it and nobody else is listening in the hallway then I dont think theres anything wrong with it