I'm going to make a joke on my colleagues behalf
What kind of joke will you make to them?
I'll make a joke about their English accent, they truly sound like idiots.
That's a little mean to think about them like that. They can't help where they're from, and accents bring lots of interesting diversity to the workplace. I hope you can find better jokes to tell instead of one that could hurt them.
Don't you watch TV? Jokes and humor have no limits.
Just because something happens on TV doesn't make it right to do it in real life.  You should try and avoid using that type of humor out there in the real world, where there are consequences for actions like that.