Flies off the handle

LOSESIT

Think of what someone might do when their temper gets the best of them—especially if they can no longer stay calm.

"Flies off the handle" is a common phrase meaning to lose one’s temper suddenly. The clue plays on the literal meaning of "flies off" as in something departing, combined with "the handle," which sounds like "it" when spoken quickly. So, if you take "flies off" to mean "loses" and "the handle" as "it," you get "LOSES IT," written as one word in the answer. It’s a clever mix of idiom and wordplay.