I, too, think the definition of air rage is a little fuzzy, but I would say it probably has to go beyond bad taste/bad manners.

Like BoSoxFan45 and TrojanHorse, I've never witnessed it myself, either. Once, I came close, though it happened after landing with the plane at the gate. One guy, who had his gear stashed further back in the plane rushed back there as soon as the seat belt light went off, pushing and shoving many of us aside in his haste. One pax took exception to this, and a shoving match ensued. I just sat back down so as not to be in the middle of flying fists had it escalated to that level, but it didn't.