also: はんぎれ
noun
half-pissed off; looking furious; about to blow their top
Slang term describing someone who is visibly angry but not yet fully exploding; a state between irritation and outright rage. Often used in casual, spoken Japanese.
See also: キレる
あの人、さっきから半ギレだよ。
That person has been looking half-pissed off for a while now.
半ギレの状態で話しかけると危ない。
It's dangerous to talk to someone when they're in a half-furious state.
キレる means to snap or lose one's temper completely, while 半ギレ describes a state of visible anger that hasn't yet reached the breaking point.
Compound of 半 (half) and キレ (from キレる, to snap). The katakana spelling ギレ reflects the voiced sound in the compound and adds a slangy, emphatic nuance.