SpongeBob SquarePants (1999)

S16E03 Squidward's Tough Break

After a knock on the head, Squidward wakes up with no memory of his past life. Without his usual cynicism, he embraces a bold new identity as a rugged tough guy. He starts talking in a gruff voice, wears a leather jacket, and acts like he’s ready for a fight. SpongeBob and Patrick are baffled by this strange transformation. They try everything to jog his memory, but Squidward seems happier than ever—until a familiar clarinet melody finally brings his old, grumpy self back.