err, explain to me how that is insulting? good refers to something being, you know, good. and US-of-A is short for (you guessed it) United States of America.
The whole "US of A" thing is a sort of... southern... slang term. It implies that we're all a bunch of rednecks or something.
This is Bob Barker reminding you to help control the Canadian bartender population — have your Canadian bartenders spayed or neutered.