It turns out that sex is just so thoroughly unsexy that your brain has to switch bits of itself off just to get through it.
According to a study of 90 female university students in the Netherlands, when you're turned on, you're much harder to gross out.
The women were asked to watch either a sports video, a neutral video of a train or an erotic film, then perform a series of disgusting acts designed to elicit different types of disgust. The acts were pretty disgusting too, including things like sticking their hands in a bowl of "used" condoms (not actually used, just covered in lube) and even putting on a shirt that they were told was worn by a paedophile whilst committing his crimes (it wasn't).
They found that the participants were much more chill about the whole situation when they were sexually aroused. Similarly, in another study with men, it was found that they were much more likely to have sex with a morbidly obese person when aroused, even if that wasn't what they were into in day-to-day life.
It's thought that this dampening of the disgust response is to get over a lot of our survival instincts to do with disease control and contamination. Usually, it's a good idea to stay away from someone else's bodily fluids, but for the purposes of reproduction, swapping substances is kinda the name of the game.
So, next time you have to take the bins out, it would be a good idea to get yourself warmed up first.