In the Pokémon anime, the episode where Jigglypuff gets angry is "The Song of Jigglypuff" (episode 36 in the original series).
In this episode, Jigglypuff tries to entertain the other Pokémon with its song, but they fall asleep before it finishes. Frustrated, Jigglypuff uses its marker to draw on everyone's faces while they sleep.
This episode is a classic and memorable one for its humor and Jigglypuff's adorable yet grumpy side.