You choose the rock

You smile at the boys and say "I'll change behind the rock, boys. Thanks for your offer, though..." You wink at them as you walk behind the rock, almost 100% certain they're going to gape, and deciding you'll give them a show worth remembering as long as they're going to. With your bag in hand, you stride confidently behind the rock. It blocks you from the view of anyone on the beach except anyone who would be looking deliberately.

You pretend to look around (not looking at the path back from where you came), and quickly take off your tank top and place it into your bag. You take a moment to turn and tweak your nipples, and sigh, knowing the guys will be watching and ogling you now, but you don't want to spoil their fun just yet. You slowly peel your shorts down your legs, and you take a moment to shake the sand out of it before you put it into your bag as well. Your right hand runs up and down your thight, and you run it teasingly over your slit, shuddering in pleasure, although this was not as much for the guys' benefit as it was for yours.

And finally, you slip your panties down your legs, your backside to where the boys most likely are, knowing they're getting a great view of your naked ass and back. A devlish grin comes over you as you think about how you're going to 'catch' the boys peeking at you. You ball the panties up in your hand and pretend to drop them behind you, and as you kneel to pick them up, you see the guys all ogling you....

Your hands quickly move to cover your breasts and pussy. "No! You bad boys, peeking in on me while I'm trying to change...go away!" The guys take their measure of you, eying your barely covered body, and you can see their hesitation as to whether to go or stay - it's not like your bikini would cover much more. Your hand start to waver as the guys eyes' stay on you, and if they stay much longer you might just drop the pretense and let them see everything...