Catch their eye and shake your head No. Later on, discuss why you suggested that they stop. Suggest that they think before they speak, and one of the things they should think about is how they would feel if they heard or saw someone else saying or doing what they did.
I've remind my teenagers to "Play the tape all the way out, think before they react or speak" all the time. I've also gotten them to understand some sign language so we can communicate beforehand. Consistency is the key. LOL