Accept the fact that they are going to stress you out. If they start to really get to you, try to go to another room, fake a phone call, or say you have to go to the bathroom. This way, you can have a minute to just focus on your breathing and calm yourself down. If you have some sort of token like a coin, or marble you can keep with you to hold on to that would be great. When you get stressed just reach in your pocket and hold it and focus on how it feels in your hand.