Does "irregular verb" have some metaphorical connotation I'm not aware of?

Yes. In the context it describes a situation when the same condition (characteristic, feature, position, etc.) is evaluated very differently depending on whether it's held by the speaker himself (I am), someone close to him (You are), or a third party (He is).

Here is a crude version: I am an original thinker, you are a weirdo, and he is insane.