your/somebody's blood is up

(one's) blood is up

One is in an angry, aggressive, or violent mood; one is looking or ready for a fight. Everyone in the office knows to avoid the boss when her blood is up.
See also: blood, up

your/somebody’s ˌblood is ˈup

(British English) somebody feels angry and aggressive: Normally, he’s a quiet man, but when his blood is up he can be very violent.
See also: blood, up