Enforcement backfiring?

Report, mute, block, don't engage. Enforcement team will be dealing with him provide you don't do any false reporting or it will backfire on you.

Every report is reviewed by Xbox Enforcement staff, and excessive false reporting can eventually backfire on the reporter and land them a suspension instead.

It is best to not respond to any messages these types of people send you, and proceed to mute and block so they'll bother you no further.

the secret is to not even try for it

To even further prove my point, I was just playing TDM on Hijacked. I went underground in the beginning of the match and killed a guy then picked up his gun. The whole rest of the match he kept coming down to kill me and was successful sometimes but I killed
him with his weapon over 12 times and did not get a single backfire medal. I'm thinking Treyarch screwed this up. Which is sad because I only need 6 more backfires to get the master of humiliation title.

I think this a rather difficult challenge. Are you sure its the same person you took the weapon from?

To me, it was pretty tough to even keep track of. I seldom remebered who's weapon I was using ... only that I would go back to the same area hoping they were repetative types.. I just had to keep working at it until it gave me credit.