Tattoo Electronics
northwestern.edu
northwestern.edu
Once you have your key of identification implanted you just created a seriously disturbing incentive for someone (without a reader to clone your RFID) to do you grievous harm when they simply want to steal your stuff.
It probably won't happen to you or many other people but it's enough of a concern that I'll put up with the occasional misplaced key instead.
tl;dr I'd love to hack your tattoo and get in your front door.