Operation - Peek in the Woman's Bath Urusei Yatsura : Season 1 Episode 124

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.