Ladies, for your own sake, please stop having sex. You're just turning yourselves into terrible potential wife material with all this slutting around and no-strings physical pleasure. It should embarrass you. In fact, it should make you take stock of the direction your life is taking. You're hellbound. Or at least spinster-with-cats-bound.
Take poor, used-up Anna Faris's character here. She's "slept with" 20 guys (that's what they call it in this PG-minded, R-rated thing). And she may protest that she's been a sexually active adult for over 10 years and that she dated all of these men with intent to turn it into something more serious and only ever had a couple one night stands and wasn't the kind of girl who can't stop saying "yes," but that doesn't excuse her one-fresh-male-sex-partner-every-six-months-like-a-streetwalker lifestyle. And she knows it.
She enlists horny neighbor Chris Evans to help her locate all 20 of her past dalliances so that she can determine who among them, if any, are finally Mr. Right or if she's doomed to a life of meaningless casual humping. Just like her -- and, really, like all thoughtful people -- he has also kept a tally of his sexual contacts and is already up into the 360-something range. But the movie doesn't care about that. He's just being a guy who looks like Captain America and possesses a functional penis. Meanwhile, those 360 women he did it with? Total whores.
Some of the old flames Faris finds are still losers or too careerist or too gay and time is running out. The movie never explains exactly how time is running out. But it is. Maybe they edited out the part where it's discovered that if she has sex with even one more man she'll turn into a column made of sea salt. Maybe they didn't edit out that part. Maybe I just missed that part when my mind wandered off to a faraway place populated by movies made for actual adults instead of for children who giggle uncontrollably when someone utters the word "boobies."
In the end (here comes the spoiler you learn from watching the trailer that explains the whole film in two minutes) Chris Evans turns out to be the guy she never knew she wanted. And not because he's great at having tons of sex or because he looks like Captain America, but because he's soulful and real and shirtless all the time and she's exhausted. Kind like how you'll be if you sit through to the closing credits.