There's an entertaining trot through the annual Bad Sex in Fiction awards in this link. My view is sex doesn't work particularly well in the written word, no matter how good a writer you are. I've also always thought it's not a spectator sport - pornography - but that's a different discussion. The awards are restricted to sex in general fiction, pornographic writing is excluded. http://www.bbc.co.uk/news/entertainment-arts-42113877
Giles Coren the Times restaurant critic won a bad sex award as did the late A A Gill who was the Sunday Times restaurant and TV critic. Gill's was for a 'necrophiliac bestiality' scene in one of his novels. Makes one wonder about restaurant critics.