A term for a poorly written sex scene, most commonly in fanfiction or sometimes original Internet works, describing sex scenes that are badly done, unrealistic, and pathetic. This can be because the characters are out of character, or if it is full of errors or generally badly written. The term was coined on fanfiction.net combining 'sex scene' and 'sucks'. It is usually used by people supporting better writing and good grammar.
Person One: Wow, that was horribly clichéd and unrealistic sex!
Person Two: Yeah, what a sux scene.