When writing a sex scene, I first try to discard any self-consciousness about what others might conclude. I work out where on the sliding scale between laughter and seriousness I want the activity to take place. What is the level of trustingness, and on whose side does power lie?
Each generation will mock the previous one because each generation tends to imagine that its attitude to sex strikes just about the right balance; that by comparison its predecessors were prim and embarrassed, its successors sex-obsessed and pornified.
And so writing about sex contains an additional anxiety on top of all the usual ones: that the writer might be giving him- or herself away, that readers may conclude, when you describe a sexual act, that it must already have happened to you in pretty much the manner described.