Gear Fighting is fighting other gear users with the player's gear. Simple! However, it's not all about what gear they own. Even if the player has the best gear, they can lose to someone using an item as simple as a Hyperlaser. A lot of people say that using gear glitches in a fight is unfair, but it's not.
A flying gear is something that the player pretty much has to own to get anywhere. An example is a flying carpet (the most used one is the Rainbow Magic Carpet). Once they've got that, the player can sort out combat gear. If the player can't afford the Scroll Of Sevenless, just get some basic stuff. The Medusa Head, the Hyperlaser Gun, and the Harpoon are all good choices. The player should also get every free item, as it may turn out to be a good counter for certain items.
Some of the most important items help the player in fights. For example, carpets will counter the stun effect of the Heatbreak Cake. A suggestion is testing everything the player owns, to see what it counters and how.
Of course there will be flame wars. When one fighter beats another, it's usually flame time. How to win a flame war: witty insults, and a good memory. Why does the player need a good memory? So they can remember all the details of your fight, and bring up EVERY LAST MISTAKE THEIR OPPONENT MADE. Just don't use stolen insults, or they'll look pathetic.
Another obvious one. There are plenty of gear fighting groups. Some of them have KOS (Kill On Sight) lists. The player will probably see the names of certain groups popping up in different games.