and "gangster," meaning proffessional criminal member of a family or group.
Combined the words mean "Criminally Evil Mirror Image."
Or: "If you contiue to mistake kindness for weekness you will meet the DoppelGangster."
This can also refer to a friend that has a more street-oriented style than you:
"My Friend JC may resemble me, but he it's more like having my DoppelGangster around."