The old adage "what goes up must come down," when applied to sex, is perhaps better rephrased: "what cums in you must come out."
This is what we've termed the "sperm-slide:" the unpleasant feeling of semen rushing back out of you when you stand up after sex. This sometimes occurs after a delay of several minutes (up to half an hour!), and the elapsed time only makes it more awkward when the cum-gush comes.
Ugh, I experienced the worst sperm slide on the way to campus this morning. And I have horrible sex dreads. I feel like everyone can tell I had sex before class.