Loose Cannon
Someone known to fly off the handle at even the smallest obstacles. Usually someone like a Cathy or a Catherine. This type of person can be quite dangerous, and have been known to mow down pedestrians for pleasure.
Example:
Did you see that loose cannon? She just ran that dude over for no reason at all, like a real danger in the shadows!
Did you see that loose cannon? She just ran that dude over for no reason at all, like a real danger in the shadows!