Vegetarians don't eat meat

My mate Stuart is a funny bloke. He's an insomniac, he's dyslexic, and he's an atheist.
He's single, unemployed, and lives all alone in a small basement flat without even a pet for company. Also he's vegetarian and teetotal, and he doesn't touch caffeine. He's pretty anti-social, actually.
I went round to see him last Sunday. As I walked up the drive, his dog started barking. His wife answered the door, and we went upstairs to their living room. He was in a bad mood because he had overslept that morning and had been late for church. He had a bit of a hangover, as well. Over a cup of coffee, he told me about the wild party that they'd had at his house the night before. They'd had a barbecue in the garden with hamburgers and hot dogs. One of his favorite pastimes is crosswords, and he spends his entire lunch break at work doing them.
'So how are you, Stuart?' I asked him the other day.
'KO, mate, KO. How about you?' Anyway, as I said, Stuart's an insomniac, dyslexic, atheist.
So the joke is that he lies awake all night wondering about the existence of dog. Get it?