Referred to as being either:
1)Completely enraged to the point of beating up/freaking out at someone
2)So compelled and psychologically brainwashed that
one begins to yell in German
and conduct a mass genocide of innocent Jews, homosexuals, retards
Can also be enhanced/more specific by adding
the suffix "on someone" or "on your ass"
Dude after Mike insulted John's mother, he started going Hitler
on his ass.
After seeing his Dad's old communist and Neo-nazi friends, Greg began going Hitler
on some of the kids during recess.