So I want to quietly kill Motor Runner, get the parts for the BoS, then get outta there. But, every time I try to reverse pickpocket dynamite on him, it freezes after he says "oh s**t!" and then I have to turn it off and back on.

help?

Unless there's no one in the area, reverse pickpocketing dynamite will not be a "quiet kill" and WILL alert nearby fiends. You should try getting a sneak attack headshot with a silenced sniper or something. That way, you don't even need to worry about that issue.

if you're [HIDDEN] then you will not be attacked actually....

anyway I just went around it by planting 12 frag mines around him and setting them all off at once (it took that many; my first try I used 10 and he didnt die).

Why are you reverse pick pocketing him/being stealthy?

I just waltzed into the Vault, shot the guard chick in the face with my trusty Gobi using HP rounds (HED ASPLODE!!), and then systematically wiped out every last Fiend in that Vault, and finished by punching Motor Runner to death.