It was appropriate for the pool. When I (F) was about 16 I was going to a friend's (M) house to hang out with our mutual friends group. My dad didn't like it when I went leave the house wearing a tank top. He insisted I get changed into something more appropriate for my friend's house.

Now, this was during Australian summer and my friend had a pool, so said "OK" and came back in a bikini. Dad let me wear the tank top after that.

TL;DR Dad didn't like me going to a friend's house in a tank top at 16, so I changed into a bikini.