I am absolutely sick of hearing my teenage students adopting the voices from Little Britain. Sometimes it is like teaching in a madhouse. I used to enjoy Little Britain but only as something I could relax with after a hard day's work. But now it's everywhere. What's more, the more I get annoyed, the more they do it.
I know what you are talking about because I have the problem, too. Your reaction to them is part of the problem; if you get wound up you can't really blame them for keeping at it because winding you up is fun. Don't get wound up as becoming emotional severely hampers your ability to reason.
It is likely that when they see that their behaviour is not having the desired effect they will stop. Stay calm and use choice and sanctions to manage the situation.
Dilemmas should be emailed to Donald Short at email@example.com