Its all about respect, really. Showing respect for your fellow players, in whatever situation it is, PVP, or whatever. If you take the weapon, have an IC REASON for it. Be respectful in knowing that they will come looking for it later (if you leave them to be raised or healed or whatever). Don't just take it "just because". Don't just take it to be an OOC a-hole.
My most Recent AMPC had an obnoxious AB, so I disarmed people all the time. I got ahold of 3-4 enchanted weapons. But I had no IC reason to keep them, so made sure I dropped them after encounters or if I was fleeing. Sure, I could have kept them, but ICly wasn't really any reason to, and I showed respect for their time and effort in aquiring the item.
All about respect. Respect others time, RP, and efforts, and hopefully in the end you'll be shown the same respect when tables turn. (Of course won't ALWAYS happen, but we can hope!)