aka: Thread Hop
A term for what a person is doing when they read only the first and/or last post of a thread, then jump to the bottom and make a reply. Nine times out of ten, they'll repeat something that was previously discussed or that the thread has long since moved on from. The cool thing about threadhopping is that if you spot a compulsive threadhopper, you can insert commentary about them into a thread which they will never read. In general Internet etiquette, skimming the last page or two of a topic before entering it is considered minimally polite, as is asking if what you want to talk about has previously been discussed.