Question

Why is the following sentence an irony? "Naming a Chihuahua Brutus"

Answer 1

The word Brutus usually refers to something big and powerful, in case is dogs.

So, if a dog's name is Brutus, we might expect it to be a big dog.

But on the other hand, Chihuahuas are the smallest dogs in the world.

I have attached an interesting image. The name Brutus would have suited the black coloured dog.
A Chihuahua (the smaller dog) is shown beside him.
As you see, the name and personality don't match.

So Chihuahua being named Brutus is an irony in itself.