Someone talking to you while you take a shower.
This one is also tricky. All the females I asked said if their spouse or children do it, they have no problem, but a co-worker (if you have to shower after work) does it, or a gym member (assuming you do it at the gym) does it, then it's quite uncomfortable. This acts defines social bad manners.
Five males said not uncomfortable so long as it is a female. Two females said uncomfortable with unknown males and three females declared uncomfortable with either male or female acquaintances or strangers. All ten persons are okay with family members or spouse.