What is an emotion that people often use to protect themselves?

Pretty sure it's anger.
But another thing you can do if your in a tough spot and don't want people to know what your think just act emotionless. Keep your face straight like a blank piece of paper. If some one tells you something to make you cry imagine your wife/husband, kids, boyfriend/girlfriend, pets, good grades, just find that happy subject. And if they try to make you smile think of bad things. Like famine, drought, disease, hurricanes, tornadoes, earthquakes, fires. But that's just kind of random lol.
Really what you need to do is just be your self. If you want to laugh, laugh. If you want to cry, cry. Smile, sob, scream, roll around on the ground. Don't hide yourself away. If you want people to like you then they need to like you for who you are. Not for you acting like some one else. After all... God made you an original, why die a copy?