Sex is only funny when you're having anal sex while talking to you mother on the phone.

Sex is only funny when you look up and see your pet watching what the two of you are doing.

*bump*

Sex is only funny when one of the kids knocks at the door while you're just getting really close. (Okay, I'm using the word funny in a little different way. :shrug: )

Sex is only funny when the kid calls out and asks you "What's that slapping?"