From Longman Dictionary of Contemporary Englishlose itlose itspoken informal a) SHOW A FEELING OR ATTITUDEto become very angry and upset She completely lost it with one of the kids in class. b) CRAZY (also lose the plot) to become crazy or confused I could see people thinking I’d totally lost the plot. → lose
Examples from the Corpus
lose it• After her mom and dad were killed in the car accident, Ginny just seemed to lose it.• Why try and pressurize myself into losing it?• Whatever Brad said must have made her angry because she totally lost it.• In fact we had never lost it.• Poor guy, he lost it.• They will not know why you have lost it.• Love, love that had always held pain through fear of losing it but had finally become a torment.• Pete just lost it completely and started shouting and screaming at us.• If they lose it, they will probably lose their majority.• Maybe he had lost it when running away from the fracas of metal and hollow clacking of gunfire.• You really lose it when you get around your family. 