S1E124 : Operation - Peek in the Woman's Bath

Ataru takes a bath at an old-fashioned sento (along with Cherry), where he tries to peek on the girls' side, where Lum, Shinobu, Sakura, Ran, Ryoko, Ryunosuke, Benten, and Oyuki are having a private party. But soon the Stormtroopers and even Mendo find out about Ataru's plan.