I would have to say a bunch of them saw her boobs at the same time.
We were dating at the time so she was my girlfriend. We lived in an apartment complex hung out with a bunch more or less around the same age. A bunch of us were hanging out by the pool sun tanning, swimming, drinking beer and so on. She and a girl friend decided to sun tan on the lounge chairs. When they turned on their front, they unhooked their bikini tops so there won't be a tan line. So basically lying there with only their bottom on with a bunch of hot blooded male watching them.
One of the guys decided to take two handful of ice from the cooler. Sneak over between the two chairs and dump the ice on their backs. It was like that epistle on MASH where they dropped the shower tent wall on Hot Lips. Everyone was waiting to see as he was sneaking over with the ice.
Both girls popped up and flashed their boobs to group before realizing then covering up with their hands. It was a cheap thrill they saw their boobs. Boyish pranks something to really not to get upset about.
My girl friend did have the nicer pair which I told her afterwards. They saw what I have been playing with.
