The way I see it, it's abusing players with things they have no access to, that you got handed down, or causing a major mistake on their part, half the time irreversible. Examples of this are conning someone into killing an NPC, pulling the levers in the catacombs (people that do that deserve a fiery death), or just blocking their path to the boss somehow.
Now, Many people see gear as an integral part of griefing. I, however, don't. I see dark souls as a game where, yeah sometimes you have to work hard for something, but if you can use it at a certain level without any troubles seeing as you have the stats for it, why shouldn't you? If you worked for it, I say go nuts. The other players have low level gear? Not your problem. you worked hard for it didnt you?
I know I know, it looks like I'm defending myself on my griefing.. but I'm just expressing my point of view. I mean.. Say a kid goes through a bunch of NG+ to get slaps for amazing armor and weapons and is only level 10? Why not allow him to use the fruit of his harvesting to his heart's content?