After being rejected by a crush, a boy might not remember her name unless he is forced to recognize it. This is because by using repression, the boy pushed the memory out of his conscious memory in order to dull the pain.
A man in his mid twenties might eat a snack from his childhood to comfort himself after a long day. This is an example of regression because he is seeking comfort in behaving as he did at an earlier stage of development.
A man in a relationship might tell his girlfriend that he thinks she wants to break with him, when really HE is the one who wants to break up. This is projection because he his acting as though his undesired thoughts are really hers.
Boys in elementary school often attempt to hide their feelings for girls by acting out in negative ways toward them. This is a defense mechanism called reaction formation, which is used to conceal forbidden desires by presenting the exact opposite.
A teenage boy with anger issues could channel his anger into a sport such as football, instead of acting out in violence at home. Sublimation can be characterized by using positive coping skills in place of negative ones.
A teenage girl might present anger toward her mother after a fight with her boyfriend. This is an example of displacement because the girl is taking her anger for one person and placing in on another who has nothing to do with the initial trigger.