Say a gang of many men beat a single guy Tom. Tom is a right guy but the gang is of cheap mentality. So, Tom wants to use an abusive and demeaning word for the gang and says you all are "xxx". He wants to say them that they all don't deserve to be called a man (they are cowards). Can the term " impotent " fits the context of Tom or any other term is used in such context? What's the term that's generally used by guys in Tom's shoes to abuse the gang?
Impotent doesn't fit. NVZ is right. Bullies is the best term. They aren't impotent because they were able to beat him up. Even if it fits, it sounds pretentious.
Cowards, which the OP mentions, could also fit. "It took all of you to beat up one guy, you bunch of cowards!" or using sarcasm "You guys are brave. It only took your entire gang to beat me up."