A dweeby, shy person. Can be used as an offensive term or an affectionate term depending on the context it is used in.
Person A: Did you see him trying to ask her out yesterday? He was being such a purk!
Person B: I know, right? I've neverseen anyone so nervous just asking someone on a date.
Brought to public attention by Bob Woodward and Carl Bernstein in the book on the fall of Richard Nixon, All The President’s Men, ratfucker was Nixon’s term for a political operative who sows chaos among opponents; an agent provocateur. It is thought to have originated among campus political rivalries at USC, and seems to have some usage in the US military.
Along with Nixon’s other ratfuckers, Roger Stone caused fights at otherwise peaceful Democratic Party protests to generate a false narrative that the Democrats were violent and dangerous.