When I was younger (M18) I was at the beach with some friends and one of them (F19) was wearing a different style of bikini that I hadn’t seen before, it didn’t have any shoulder straps and was help together by a buckle in-between her boobs. I took notice of it and we went about our beach day, we had been laying next to eachother in a shade tent in the sand for a while in silence just relaxing and I turned my head in her direction just to make my neck more comfortable and her bikini had shifted and one of her nipples was out, so I just lay there for a few minutes admiring her gorgeous breasts until she sat up and realised what had happened with her bikini and fixed it but she still didn’t know I saw. If she looked at my pants she would have seen the bulge she gave me.