Dollar -- Oh, OK, you haven't been here very long.
Some of these predate me, so there's probably history beyond what I'm giving you. But it'll serve as a start.
An opus is a "final post" where the poster tells everything that's wrong with Free Republic, or Jim Robinson, or the quality of the posting (usually a decline from the 'good old days') or blames the Admin Moderator or some shadowy cabal on FR for their posts not being received well, etc. etc. Basically they're calling a Waaaahmbulance for themselves.
There were two main types that happened during my limited time here.
The first was in reaction to a long standing complaint of some of the pro-Evolution posters on the crevo threads. They would be subject to having their homepage disappear without warning (and apparently it was either Jim Robinson or a high up admin doing that, and it *IS* his site)...
Or having the mods take the side against them during flamewars, with arbitrary capricious enforcement of rules, etc.
So a number of them ended up publishing various opuses, that all they wanted to do was save FR and/or the conservative movement from the vile calumnies of the left that all conservatives are a bunch of Neaderthal Luddites, etc.
A number of them are practicing scientists and / or at govt. labs and / or real research Universities; several have *very* impressive credentials (not just PhDs but from, or affiliated with, top World-class institutions) but in the interests of FR anonymity I will not elaborate: people have been banned over posting the real-life names of FReepers, even when the person "identified" had been posting in public elsewhere under their real name and not hidden the identity.
Most of these people went over to a site they founded called Darwin Central. This name was chosen explicitly to tweak the nose of people with whom they disagreed, since Darwinism proved such a bone of contention: it started out as semi-tongue-in-cheek but as hurts deepened so did the seriousness. It is like FR in that it is a political site, but with a MUCH stronger libertarian emphasis, and much more robust discussion of hard science from a scientists' viewpoint. There is also a strong subset of atheists there who are NOT shy about sharing their opinions, much as there is a STRONG subset of Christians here who are not shy about their opinions. There don't seem to be as many denominational flamewars among atheists, btw. ;-)
They seem to have been upset as much by the maltreatment, as having to answer ad nauseum the *same* set of questions seemingly cut-and-pasted from Answers in Genesis or similar sites, by the SAME people, no matter how many times the subjects had been discussed or answered.
The other type of opus occurred in what is now known as the Bug-Zapper thread, which happened in the pre-runup to the 2008 election, when a number of people were pushing for Rudy Guiliani to get the nomination. Jim Robinson was and is dead set against this, and people started getting zotted. A number of people flamed out in truly spectacular fashion, hence the name "bug zapper".
As far as pissant -- he was an anti-Palin troll, who finally got the zot for a post I will not reproduce, where he rather graphically accused Gov. Palin of an active lesbian affair with Tammy Bruce. ZOT.
Any other questions, look up FReepers with older signup dates than me. They'll be able to tell you all you want to know.
Cheers!