Door Gangster

Someone who acts like the toughest person on the planet as long as there is a physical barrier between them and the person they are trying to intimidate. Primarily in a jail setting, but can be interchangeable in all of life's scenarios.

The guy in cell 36 is the biggest Door Gangster. He threatened to spit on me until I opened his cell door, then he went to his bed and laid down like a bitch.