But I'm not used to it, I still find it offensive. After all, rats are extremely clean, intelligent animals. I had pet rats for many years and they are polite, gentle wee creatures.
Small dogs, not so much.
For a start small dogs don't know they are small dogs, they think they are big dogs. Huge, scary dogs. Mungo, all two-ish kilos of him, is convinced he is mastiff-sized. In his mind's eye he has fangs, fight scars and wears a studded collar.
In real life Mungo is weedy, with several teeth missing and he wears a harness with a label saying extra small. Sometimes he wears a silly T-shirt with "guard dog" on it and everyone laughs at him.
But he's a real dog. He's even a bit of a hunter - he caught a rat once. It had been dead at least two weeks when he pounced on it, but it's the thought that counts.
In fact the only thing alive about his quarry were the maggots. They were very lively - I hadn't realised how fast maggots could move until that morning, 3am I think it was, when I put on my bedside light to see what Mungo was crunching on.
Those maggots were fair sprinting up my duvet towards me. And they moved even faster once I had rolled up my duvet, dog and his prey and flung the lot out the back door into the dark. They flew.
Mungo also likes to have a good old-fashioned "real dog" roll in stinky things. This is where I think small dogs are way more offensive than the biggest of big dogs.
I used to own great Danes. When it comes to rolling in stuff they are no slugs either.
Your average great Dane can smear itself with about 1.5kg of horse manure, or a close equivalent in putrid possum carcass. Now, when a dog is packing that much gross material, you can see it coming. It's smeared over a large area, you can't miss it. You have time to run, grab a hose and do battle.
A chihuahua, by comparison, can only coat itself in a few meagre grams of crud.
There's simply not the surface area for much more.
A few grams of crud, you do not see coming. It sneaks up on you, you don't notice it until it's right under your nose.
On your lap, in fact, snuggled right into you on your favourite chair, in your comfiest pants and T-shirt, all now smelling truly gag-worthy.
My smallest chihuahua is one of those "teacup" varieties. While basically meaning he's tiny, the word "teacup" brings to mind all manner of genteel images: high tea, the tinkle of teaspoons, "one lump or two?"
In reality Hugo the "teacup" chihuahua is the master of the immense burp. Hugo has a burp that belies his size. When Hugo burps in the kitchen, we hear it in the bedroom.
And he does it often. His signature move is to run up, tail wagging and looking cute, wait till you reach down - way down - to pat him and ... burp.
Pretty much in your face. I tend to warn people who reach to pat him, exclaiming "oh he's so cute". No, I tell them, he's not cute, he's just small.
But the worst culprit by far is Milo the miniature pinscher. He thinks he's not only a big dog, but boss of all he surveys.
Which in truth can't be much because he surely can't see a lot from down at his level. However, if anything bruises his ego he has a unique reaction.
He will - there's no way to put this politely - he will do his business in your shoe. We call it the shoe poo.
If you go to put on your sneakers and there's a tiny dog log in one of them, you know you've upset Milo. And it does pay to check, as my husband once realised, part-way round the supermarket.
So just a word of warning - if you have called Milo a rat recently and he's heard you ... check your shoes.