No one enters into a relationship thinking, A few years from now, we will have sex only as frequently as a total lunar eclipse. And it will be nowhere near as spectacular. Yet for a variety of reasons, on any given night, watching Keith Olbermann may feel more compelling than tearing each other's clothes off. Which is why you just might want to consider kicking Keith — and your television — out of your bedroom (more on that later). Sure, everyone's sex life waxes and wanes, says Terry Real, a family therapist in Boston and the author of The New Rules of Marriage, but a steep and permanent decline is not inevitable. And arresting that slide can be as simple as undoing some all-too-common sex don'ts. Check out these please-don't-go-there sex killers and see which ones (be honest!) could be cooling your jets. I'd say the biggest sex mistake would be having sex with Paris Hilton, who knows what she has. You are probably better cutting it off if you do.