One of my possibly annoying habits is inserting pop-culture references into random conversation. I have a large store of song lyrics and movie quotes swimming around in the back of my head, and they have a tendency to pop out when they seem vaguely relevant. A lot of the time I don't even realise I'm doing it until too late.
This can be particularly annoying on IRC, where I am quite capable of spending hours doing nothing but interjecting the occasional line from a song into the conversation.
Paradoxically, when that meme was going around a few years ago where you had to answer a series of questions about yourself using only lyrics or quotes, I was unable to do it. I guess that has something to do with how much I suck at improvisation when I'm put on the spot. I can free-associate when the pressure's off, but sit me down and order me to think of a relevant quote for something specific, and my brain seizes up.
By far my favourite, and most common quote, however, has to be this (although I usually misquote it slightly):
I say we take off and nuke the entire site from orbit. That's the only way to be sure.
It's applicable to so many different situations.
My favourite quote's got to be Jules' (Samuel L Jackson) in Pulp Fiction:
"The path of the righteous man is beset on all sides by the inequities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee."
...which is, by itself, a quote from Ezequiel, but the way it's said in Pulp Fiction puts it in a whole lot more context than I could describe here ;)
Not really applicable to lots of situations, but when it is, the conversation is usually over after the last word.
Well, it's not all from Ezekiel 25:17: Tarantino and Avery added a bunch of stuff to make it sound better. In the process, they completely changed the meaning.
Ezekiel 25:15-17 (King James Version): "[15] Thus saith the Lord GOD; Because the Philistines have dealt by revenge, and have taken vengeance with a despiteful heart, to destroy it for the old hatred; [16] Therefore thus saith the Lord GOD; Behold, I will stretch out mine hand upon the Philistines, and I will cut off the Cherethims, and destroy the remnant of the sea coast. [17] And I will execute great vengeance upon them with furious rebukes; and they shall know that I am the LORD, when I shall lay my vengeance upon them."