Guard mentality is the mentality of a person on a defense oriented state of mind. He (or she) interprets sentances stated towards the person in a negative or insulting manner.
Dude that guy there has a total guard mentality
the mental state in which one feels they should have grown men stripped naked with only hoods on their head and pretend to machine gun their genitals.
Mental state dissipates once photographs air on 60 Minutes.
My God, did she just put that prisoner's ass on the other dude's head? Is she pointing at his junk while taking a picture?
Yes. She has a guard mentality.