>Relatedly, I have certainly had the experience of remembering something as being hilarious only now to be turned off by how clearly sexist it is

That's part of the humor.

Plus a lot of people conflate sexual with sexist -- thinking about sex and working towards humping is considered automatically sexist in protestant-derived cultures (who'd rather we were all asexual and only interested in sex and in the other sex under very specific situations -- marriage, back in the day, a relationship, today).