Usage patterns
〈人〉を臆病者と呼ぶto call someone a coward
Everyone called him a coward for running away.
臆病者のくせにdespite being a coward (used mockingly)
For a coward, you sure talk big.
臆病者扱いするto treat someone as a coward
I think it's harsh to immediately treat him like a coward.