Just for example, variants of:
Always cheat and Have plan to kill everyone from training classes have been brought up in cases.
Your defense attorney has to present a coherent story of why you acted the way you did according to the jury research literature. The DA will present his or her coherent version. If theirs started with 'he was going animal' - that will stick in the jury's mind.
Pax's animal - fighting like a cornered cat gives a metaphor of defense as compared to being off the rails.
My favorite Glock example - went to a new range to try it out. The SOs there check your gun before you shoot to see if it is ok. High class outfit. The guy ahead of me had the back plate of his Glock replaced with one with the Punisher skull logo. Now in an ambiguous shoot, when that gun is shown to the jury - oh, dear - and you shot the teenager (there are several cases I know other than the one you are thinking about) because you felt you had to be an animal, wanted to cheat and had a plan to kill?