a loose cannon

a person who cannot be completely trusted because their behaviour is sometimes strange or violent He's seen as a loose cannon by other team members. If anyone's going to get into a fight, it'll be Pete.

Common Names:

Name	Pronounced	Usage
Shinobu	shee-no-boo	Japanese
Ebbe	EB-be (Swedish), E-bə (German)	Danish, Swedish, Norwegian, German (Rare)
Nicoleta	-	Romanian
Lowell	LO-əl	English
Tina	TEE-nə (English), TEE-nah (Italian, Dutch)	English, Italian, Dutch, Slovene, Croatian, Macedonian
Malcom	MAL-kəm	English