That's No Lady - S4.E29

A misunderstanding over a vacation getaway advertisement causes Patrick to think he must "get out of town" or face dire consequences. SpongeBob can't bear the thought of his best buddy moving away, so he decides to do what he can to hide Patrick's identity from his "pursuers." After many failed attempts at disguises, they finally settle on the perfect one: Patrick is transformed into a girl, Patricia, to be exact. Patricia catches the eye of Mr. Krabs and soon she becomes the most charming waitress/waiter at the Krusty Krab.