Bath / shower I take mine off. I'm an adult.
What, you think I'm gonna take some time to wash my toes and my balls but I'm not gonna wash that bit of my left wrist because the watch is always in the way? And I don't need to know the time for any washroom activities, I know how long they take.
If I'm showering at a public place and don't want to leave an expensive watch in my bag/locker I will just keep it with me. But I generally wear a cheaper digital watch for the gym rather than a $$$ mechanical one so not too concerned about leaving it in the locker when I go off for a wash.
If swimming, I'll wear it (if metal or rubber strap). If sleeping in my own bed, I'll take it off as prefer not to wear much. Although if I'm in someone else's bed I might keep it on as it allows for a quick exit if needed... one less thing to think about...
