Generally, I hate the word RINO. In modern political discourse it serves no purpose other than as an insult hurled at someone with whom the speaker disagrees. Accordingly, I try to use it as sparingly as possible and only when it truly applies - when someone really is a Republican in name only.
Let me illustrate. People frequently use the word "RINO" as a pejorative against moderates, but that's not really accurate. Take a guy like Mark Kirk for instance. Kirk is a squishy guy who can really infuriate you with his votes at times, but Kirk is a loyal guy to the Republican party. I mean, he needs to get re-elected now and then and so he casts votes with which I strongly disagree, but Kirk is not going to go out and openly endorse a Democrat, hold pressers with Democrats where he bashes Republicans, or bail for the Democratic party if things get too difficult. Kirk is a moderate, but not a RINO.
This is to distinguish a guy like Kirk from a guy like Arlen Specter. Specter began his career as a Democrat, and only switched to being a Republican when it was politically expedient for him. Then, when it wasn't expedient for him anymore, he ditched the party and went back to being a liberal Democrat. Same basic principle applies to Lincoln Chafee and Michael Bloomberg. These are true RINOs - and they are the most faithless sort of "man" in existence, because they narcissistically and cynically use the sweat, donated money and time of countless civically-minded people and toss it aside on a moment's whim just to serve their own pathetic needs. A true RINO has no interest in furthering a larger coalition or cause - they only have interest in what they can parasitically suck out of it for their own benefit. I would not trust any of the three men listed above to watch my cat, or to watch my briefcase while I went to the restroom.
So anyway, you know who's a true RINO? Ron Paul. When he got his feelings hurt after he lost the 1984 Senate Primary to Phil Gramm, he decided to run for President. Only, he realized that he would get no attention and no traction running as a Republican, so he ditched the party and ran as a Libertarian. When he decided to go back to Congress in the mid-90s, he suddenly found himself as a Republican again. Then, after he lost his bid for the Presidency in 2008, he refused to endorse the Republican nominee for President, favoring instead two socialist loons and a confederate sympathizer. Now, yet again, Paul has pointedly refused to commit to endorsing the eventual GOP nominee and to completely rule out a third party run. Here he is helpfully explaining that after working for months to get the GOP vote, trying to hijack GOP conventions, and using the GOP brand to get himself on national television over a dozen times in debates, there's really no difference between Republicans and Democrats:
Republicans - the kind that are Republicans not just in name only - understand that teamwork is vital to getting anything done in a country as large and diverse as America. Sure we can have our disagreements and we can and should fight them out aggressively in a primary. Candidates who will not respect the will of primary voters and who will display the shockingly poor grace and faithlessness to spit on their party and willfully throw the election to a candidate from the other party - contrary no doubt to the wishes of countless of people who worked for and donated to them - are the most corrosive force in politics. They are the true RINOs, who have demonstrated themselves faithless to any cause larger than their own personal ambition, and they are unworthy of the Republican primary votes they desperately seek.