Self-deprecation

Self-deprecation is when a person speaks or acts in a way that makes them seem less important, smart, or talented than they actually are. It's usually done as a joke, but it can also be done unconsciously. For example, a person might say, "I'm so bad at math!", even though they are actually pretty good at it. Self-deprecation can hurt a person's self-esteem if it's done too often, because it can make them start believing that they aren't really good at anything.