Pick something really long, but with some nudity
Did you know that Titanic runs at a staggering 194 minutes long? I know what you’re thinking -- “Titanic is a classic, I would never have sex in front of that timeless work of art.” Sorry to burst your bubble -- or, rather, sink your bubble -- but Titanic didn't age well and your perceptions of art are as misplaced as Billy Zane's.
On the bright side, if you time it right, you can get more than a couple sexual encounters in one sitting. The trick is, you have to start immediately: the first 30 minutes of the film is Bill “Am I a real person?” Paxton searching for the Heart of the Ocean diamond. Then there’s another hour or two of bad dialogue, giving you almost 90 minutes to get through kissing, foreplay, fucking, and cuddling.
Then, by the time the “draw me like one of your French girls” part comes up, you’ll be ready for another go. Just make sure you finish before the end, it’s pretty hard to maintain a boner while 1,500 people die in the Atlantic Ocean... unless you’re me, of course. Man, still can't believe that Bill Paxton had a sizable role in this movie.