If you have sang-froid, you can keep your cool, even under stress. Your feathers aren't easily ruffled.
This foreign-sounding word is another way of saying "poise under pressure." We borrowed it from French, where it literally means "cold blood." Great athletes who do well in the last two minutes of a game have sang-froid. James Bond definitely has sang-froid. You better have sang-froid when you're taking the SATs. If you're worried, nervous and starting to crack, you've pretty much lost your sang-froid.