Guys are almost always in the mood. The best way to get revenge on a woman that uses this line on you is the next time she's frisky and you're "not in the mood" is to rub one out right there. Then you won't be in the mood for at least 5 minutes.
I knew this huge black guy who worked at the grocery store. It was around thanksgiving and it was really busy for stocking, which was his primary job. His girlfriend picks him up after he pulls an extended shift, she makes it clear to him that she wants to have some quality time when they get home. Without a second of pause he says "Nah, I'm too tired. You just suck my dick".
If I live to be a thousand I will still never be able to pull that off.
Wait until you're a little older and you've just put 10 hours in at work and then driven home for an hour in heavy traffic and then gotten home and spent 2 or 3 hours with your kids as well as household chores....you'll say that more often than you think .