A: My criticism was not targeted at anyone personally. I don’t understand why he became furious immediately.

    B: Don’t argue with him after he drinks too much beer. He is a loose cannon when he is drunk.

    Note: This idiom refers to an unpredictable person or thing, liable to cause damage if not kept in check by others. From the 17th century to the 19th century, wooden warships carried cannons as their primary offensive weapons. In order to avoid damage from their enormous recoil when fired they were mounted on rollers and secured with rope. A loose cannon was just what it sounds like, that is, a cannon that had become free of its restraints and was rolling dangerously about the deck. The earliest figurative use of “loose cannon” in print is supposedly from the Galveston Daily News in December 1889.