Bart takes a while to find the mens' bathing suit section, and even longer to find something even resembling 21st century swimwear.

We won't go into the 51st century mens' swimwear. (Let's just say they're really open-minded.)

At any rate, he finds himself a pair of red-and-yellow swimming trunks and then wanders off to find (a) Jenny, or (b) a changing room of any sort.