The 26k trick is a recent tactic used by pkers in order to manipulate the pvp system into making lots of money. The way it works is that players spend lots of time in a bounty world in order to build up their pvp earning potential. Once they reach 100% ep they usually get a friend to carry at least 26k in f2p or 76k in p2p so that they meet the requirements for risking items. Then they take turns killing each other resulting in getting a valuable idol. Many people think that if your opponent risks more than 26k in a members or free world you have an equal chance to get a good drop. NOTE: getting 100% ep only gives you more chances of getting a good drop it does not actually give you a guaranteed good drop.
Usually this tactic is done on the bounty world border so they can safe if needed. Often times this is done by clans or in teams in order to increase effectiveness.
This tactic is often seen as exploitation and cheating although it is not technically against the rules. It is looked down upon by most players for taking the fun out of pking and ruining the RuneScape economy.
On October 26th, Jagex made a solution to 26/76king by making you not able to get a good drop by killing the same person more than once.