to forget one's manners or training. (Said in formal situations in reference to belching, bad table manners, and, in the case of very young children, pants-wetting.) Sorry, Mother, I forgot myself.John, we are going out to dinner tonight. Please don't forget yourself.
Lose one's reserve, temper, or self-restraint; do or say something out of keeping with one's position or character. For example, A teacher should never forget herself and shout at the class. Shakespeare used it in Richard II (3:2): "I had forgot myself: am I not king?" [Late 1500s]