And if you absolutely have to. Still don't.
Nobody does it well because it can't be done well.
Unwelcome sex: Yes. Failed sex: Yes. The absence of sex. Yes. Thoughts about sex: Yes.
Actual, detailed I-put-my-hand-on...: No.
Spare us. Hint at it. Show that it happened, reference it obliquely. Just don't try to describe it. Ever