an abject coward
poltroon - coward
A ‘poltroon’ is a person lacking in spirit and fortitude. As well as describing somebody behaving in a way that is devoid of courage or confidence, the word also implies a sneaky and devious character that is the opposite of what is considered admirable or heroic. This term has only negative connotations as such people are generally regarded with contempt.
Gary likes to talk tough, but as soon as he’s confronted by anyone he turns into a whimpering poltroon. It’s pathetic.
Nothing great is achieved through poltroonery. You have to be willing to take risks and fight tooth and nail for something.
I gave as good as I got when my boss reprimanded me in the meeting because I didn’t want my co-workers to think I was some kind of poltroon that couldn't stick up for himself.