Irregular plurals

Irregular plurals
The Princess is fond of a piece of poetry from this book that goes as follows:

Daddy is a doofus, a doofus, a doofus
Daddy is a doofus, a doofus because…

It goes on to ennumerate reasons why Daddy is a doofus including “belly like a burger” and “combs his hair with fingers”. I think that it would be fair to say that it’s probably not Mr. Waffle’s favourite poem.

Her: Daddy doesn’t like “Daddy is a doofus”.
Me: No, I don’t think so.
Her: It makes him go like this (sticks out lower lip).
Me: I see.
Her: But I say to him “Daddy, you’re not a doofus, all the other daddies are doofi.”