Try looking for a beach that isn't used at all if you can. There's a beach here that I went to because I remembered it from my childhood and wanted to go back but had only just got the chance, I went there and found that coastal erosion had left it much harder to get down to than before - after already driving down tiny country roads - and there was no one there. Look on a map and see if you can find a spot of beach with no roads or houses by it and see if you could walk down the coast to it a bit so you're alone. I went topless on my little bit of beach and it was just like being 4 years old and able to now worry about what's socially acceptable to do with my body by female standards although I'm male, brilliant!
If that's not an option then I'd go all out and tart it up to make it look deliberate, pink trunks, pink bra, maybe some temp hair dye even and if anyone asks it's a dare.