The reprehensible practice of speaking three letter acronyms out loud, especially when in spoken form they take a lot longer to say than the words they signify: I have heard "bee tee doubleyew" used in conversation in place of "by the way". I am not making this up.
The equally reprehensible practice of brutally overusing IRC abbreviations, "emoticons", and whatnot. I mean, yeah, it's great to have interests and all, but Jesus... It's worst when they put an expansion of an acronym in parens after the acronym itself, like for example: "IRL (in real life! ;-)" What exactly is that accomplishing?
IRColalia seems mostly to affect people who, like, really =) want you to know what, like, total web GEEKS *8-) they are!!!!!!! ;-) LOL!!!! B-) See also I'm going to take five of those six exclamation points and drive them into the soft flesh under your fingernails.
Most overenthusiastic newbies (even Jon Katz) deserve the benefit of the doubt because after all, we used to be blown away by the novelty of it all ourselves.