Sgt. Frog Episode 56: Hard to (Be a) Swallow!
Episode 56 of 358 of Sgt. Frog, aired April 29, 2005, 25 minutes. Available with English subtitles and dub where released.
Episode summary
Koyuki sees a movie that convinces her true friendship is born in competition. So she challenges Natsumi to a tennis match... where the loser has to wear an afro hairstyle! Source: crunchyroll