blow (one's) cool
To lose control of one's composure, temper, or nerve. He really blew his cool when the waiter dropped his food. I really blew my cool during the interview.
blow one's cool
see under keep one's cool. 
blow your cool
 lose your composure; become angry or agitated. informalblow one’s cool
 tv. to become angry.  I almost blew my cool when the dog wet my pants leg. 
  blow (one's) cool
 Slang  To lose one's composure.