ISTP - Probably most likely to literally stab someone in the back, but not likely to do so in the speaking/other behavior sense.
When in the world would stabbing someone in the back ever be effective? If you desire to kill someone, poisoning them with a overdose natural compound would be more effective as it would appear a natural, but tragic, bodily malfunction. Or, if you're in a situation where you need to use induce death by physical trauma, a gun is much more effective due to range. A knife (or whatever being used to stab) can only be used at point blank range. In addition, why have you chosen to stab in the back as opposed to, say, slitting said person's throat?
Or, why would you try to stab someone in the back but not attempt to kill them? The average person will fight back in some form, possibly using the knife that stabbed them as a weapon against you.
Overall, the idea of stabbing someone in back in the literal sense seems rather impractical.
If a deaf INFP falls in the forest and no one is around to hear it, does it make a sound?
I'm going with ESTP. Notorious salesman who manipulate for their own gain. Once they get what they want, in goes the knife.
Not that I'm bitter...
OA, I tend to ADORE your comments...
So uh, I've got this used car that's available. Don't worry, everything about it is fine, and no it doesn't come with a warranty, but you won't be needing one, trust me, afterall I'm honest abe the used car salesman! You do like bling on your car right?