I had an incident recently when I was swimming at my local leisure centre, and a young lady in the adjacent lane shouted "what the fuck are you looking at" as I approached the shallow end.
I tend to concentrate on avoiding collisions in my own lane and look out for anyone faster I should be giving way for. I hadn't even noticed her, and if I had it would have been out of what limited peripheral vision I had out the side of my goggles.
I therefore just shook my head and laughed as I swam off.
Every time I passed her after that, she was just chuntering away.
I'm not sure if she was looking for conflict, had mental health issues, or just took an instant dislike to me, but it did seem weird given that my leisure centre is usually a very sociable place and everyone is usually very tolerant.