I mean the person who only has the gut on bullying small guys, but when he faces big guy, he will surrender and give in like a puppet.
'bully' was suggested by someone before, but it obvious is not precise enough. Any suggestion? thanks.
edit: If there isn't a single word to say such a person, what are some idiomatic terms or words for describing?
I still feel that 'bully' isn't precise enough in describing a person like that, because a bully could sometimes bully someone bigger than him, it's possible and personally I saw this kind of bully before. Besides, 'bully' doesn't carry the connotation of "when he faces big guy, he will surrender and give in like a puppet."