This story happened in 1995, a time when it was still common that women went topless at the beach in Europe. Something which has become less common since the introduction of cellphones with cameras.
A year earlier, I went out a few times with a girl. Nothing really serious, only got to 1st base with her. After she dumped me for another guy .... eeeuuuh ... I mean came to the mutual agreement it wasn't going to work out

, we still saw each other frequently cause we were member of the same sports club. Her sister was even mad at her for a while for dumping me that way, but later I heard that was mainly because she also had a crush on me.
The next summer, I went to a beach resort with my family and as it happens the girl and her family arrived at the same day too. However, we stil had to wait a few hours before our cabins were ready. The girl's mom wanted to go to the beach already, as did both sister's. The mom asked me if I wanted to join them. Really thoughtful till I found out which dummy was carrying the bag with all the towels and drinks. But hey, I was a young god in my late teens

, so nothing I couldn't handle.
When we arrived at the beach, it was already packed so we walked a bit further till we found a more quiet spot. Nearest people were about 30 feet away or so.
I put down the bag and we laid out all the towels.
Next we started to undress. I had my swim trunks on and the 3 ladies their bikini's underneath their clothes. As I only needed to get rid of my tshirt and slippers, I was already rubbing my pale body with sun lotion when I heard the mother say : "Well girls I don't know about you, but I will be going topless, I'm on holiday after all." And with that she removed her bikini top. The girl's sister followed her example instantly. The girl was shocked for a moment I guess, but since she was the only only left wearing her top, she hesitantly removed it too.
So there I was sitting on the beach not knowing exactly where to look and with a growing bulch in my swim trunks. Although nothing sexual happened, it was all "just" public social nudity, I found it quit thrilling. Also funny to see how breasts within 1 family can be so different. The mother had an AA-cup with normal sized areolas but really long and thick nipples. The sister had an A-cup or small B-cup with small areolas and small nipples, almost boyish. Then the girl that dumped me, I finally got to see her topless supporting a full C-cup, maybe even a small D-cup, with larger areolas and thick long nipples.