Ah, excellent phrase!
I recall being a teenager on my third (or fourth, or fifth!) job and having a boss take that posture with me over some trifling matter that is lost to history.
I told him exactly that: “Stick your finger in my face one more time and you’ll draw back a bloody stump!”
I lost my job (no big loss since it was K-mart), but didn’t lose my pride.
Normally I use it when someone tries to reach into the car and aggravate the Dobes but it’s pretty universal. :D
The guy who bought my dads land above my house pulled that on me and had no idea how much being poked at pisses me off.
/side note: I’m wearing a Walking Dead shirt today that says “Beware I Bite”
;)