To avenge oneself.

(idiomatic) Relaxed and confident in one's manner of presenting oneself and interacting with others; conveying the impression that one has a clear, satisfying understanding of one's own abilities and situation.

(idiomatic, vulgar) having an excessively high opinion of oneself.

(idiomatic, usually preceded by a) Harsh treatment inflicted on one who previously inflicted similar or equivalent treatment on others.

(idiomatic) To behave in a way that is likely to have future negative effects on oneself, including (but not limited to) death.

(idiomatic) To form one's personal opinions and choose one's actions without being governed by the views or choices of others; to be independently minded; to think for oneself.

(idiomatic, often ironic) One whose fame is insignificant, fleeting or imaginary.

Exceptionally timid.

To kill oneself; to commit suicide.

(Britain, Commonwealth of Nations) To praise oneself.