Maybe a lot of posters here don't go swimming very often. There's not much hiding your body shape when you swim, even if you wear one of those swim dresses. So if you're offended by fat, spotty, saggy or scrawny bodies, it probably isn't the exercise for you. Let me reassure you that you really, really don't have bums in your face while swimming (unless you're trying to get on top of people?).
And while you might occasionally have an unfortunate incident like OP's, it is rare, almost always accidental and very quick (I'm assuming she turned and moved away as quickly as possible).
What's far more common and annoying are people going in the wrong speed lane and men (always men) who cut across the lane or ignore the clockwise swimming direction and just go straight back and forth, essentially forcing a kind of personal lane within the lane and getting in everyone's way. If you can deal with those idiots, the odd bum shouldn't faze you. You only see them when people are on the way out and walking away anyway.