a) People in authoritative positions. Usually those who abuse, or misuse their authority for spiteful reasons detramental to the common good. Basically haters with power.
b) See "The Man," "The Establishment,"
c) Haters with no power can also be classified as "them people."
Scenario: You work in a chemical plant where cell phones are illegal.
Employee #1: "Man, I gotta check my myspace on my iphone."
Employee #2: "You better put that up, "them people" are on their way to the control room."
Some guy: "Man, me and my ex were supposed to link up for dinner last night, but she was surrounded by a bunch of "them people" and they pumped her head full of bullshit and she cancelled."
Worker #1: "Man, stop kissing so much ass, and running to the managers everytime something happens."
Worker #2: "I don't know what you're talking about."
Worker #1: "Whatever man, you're trying to be one of "them people."