Billingsgate is rude, abusive language. If a political debate is becoming nasty and insulting, it's good to have a moderator who will demand an end to the billingsgate.
The British term billingsgate is less familiar in the U.S. — but it's a great way to refer to a particularly coarse form of verbal abuse. It comes from London's Billingsgate Fish Market, a 17th-century open-air market where ill-mannered fishmongers hollered raucously, haggling over prices using rude and vulgar language. The word can be used for any kind of foul-mouthed vituperation: "No arguing about sports rivalries at my birthday party! It always turns into pure billingsgate!"