Glitching - Bearded Lady

Jagex apparently has never bothered to fix this glitch even though it was first found with AutoRune. Also, there is two different types of this glitch. A bearded lady created by modifying the client (as shown in this picture) will result in the character being acknowledged by NPC's as female. The ones created with a packet editor will result in the player being referred to as male.

Oh, and you can attempt to create a character without a head, but the game will not let you continue.

Glitching - Mass Spawning Zombies

The Necromancer is an interesting NPC. When attacked, it spawns a zombie, and does so 7 times before it can be attacked. However, the game developers seems to have allowed the 2 Necromancers located in the tower next to the Fight Arena to share the same "zombie spawned" flag, allowing you to simply spawn 7 zombies on the Necromancer, and without killing any zombies, go to the next floor and kill the other Necromancer.

This allows you to spawn a massive number of zombies at once. There's actually a limit to how much zombies the game can spawn. What happens once you reach the limit? Well, it gets interesting...

Glitching - Thieving the Fight Arena Guards

As you can see in the above picture, there's no option that allows you to pickpocket the guards located near the Fight Arena. However, with the use of a bot, players can somehow allow the game to steal from the normally "unthievable" guards for 30 GP. Interestingly, they could also be attacked, but only by talking to them; using a bot to attack them would bring the "you can't attack that" message.

Btw, I paid 1M GP for someone to test this out, since noone would do so at a lower price. :P