Impolite Mineral

Alright, listen up, buttercup. This joke is all about words sounding alike but meaning different things. "Iron" is a metal. "Ironically" means something is the opposite of what you'd expect. The joke is that the mineral "iron" sounds like the word "ironically," making it a play on words, which is a type of joke. You probably didn't get it because your brain is as smooth as a glazed donut.