Bad Hair Day is an episode of Aaahh!!! Real Monsters from the 3rd season.
Summary
When Krumm loses his pit hairs as the result of a "Monster Mischief Day" prank, Ickis vows/promises to do anything to get him his hair back. Ickis finds a stash of discarded "Super Grow" hair tonic in the dump and rubs it in Krumm's pits to disastrous results.