The iron buns are a body part that appear in the episode "Krusty Krushers."
Iron buns are a pair of metal buttocks that Patrick develops after a large amount of butt exercising in preparation for the main wrestling competition.
Role in episode
Patrick had previously done various butt exercises that made his buttocks strong. It is also shown that he developed them while he was sleeping. As a result, Patrick is able to generate his iron butt within seconds before the twowrestlers can "drill" onto SpongeBob and him on the bed that is in the main stadium.