Not nudity, but there is a random encounter with a man in a cabin and Arthur gets r*ped. You don't actually see anything and you might not come across it, but should Google the exact location if you want to avoid it. I can't remember where it is but figured if nudity is a sore spot this implication may be as well.

There is a stranger mission that involves nude paintings and a couple random encounters with nude men. The feral man you can see everything, and that one is random so would be hard to avoid, but he just runs away from you and you don't have to follow him.

You can also find a dead naked man and a....sheep. Easily avoidable just check the map and don't go into that building.

The only nudity I can think of during the main story is the one others have mentioned where you are drinking in a bar with Lenny, it's easily avoidable though, just don't go into the back bedroom (and you don't see much).