No weapon glitch
From Halopedia, the Halo wiki
The No Weapon Glitch is a glitch present in all games in the Halo Trilogy. It allows players to apparently disarm their in-game characters. The players' weapons are effectively deleted.
Halo: Combat Evolved
The No Weapon Glitch is not as well known in Halo: Combat Evolved's Multiplayer, but the process is pretty simple. It works easily on Halo PC, but is harder on Xbox because there is less lag. There are two kinds of No Weapon Glitches in Halo PC: one from the host's perspective and one from the client's perspective.
Multiplayer
To perform the glitch in multiplayer, you need have at least one other player to work with. Gather multiple different weapons together in a closed area, like in the Blood Gulch Base. Then, tap X (The button you have set for the "Drop Weapon" command) or E (The button you have set for the "Action" command) repeatedly over the weapons. This should make you continuously drop and pick up new weapons.
Eventually, you will not be able to drop your weapon. This is due to your weapon "phantoming." All other players in the game will view you as if you had no weapon; the player you performed the glitch with should be similarly unarmed.
If you press Tab, you may switch to your other weapon. The game may automatically switch you to your other weapon after a certain amount of time. When you have switched weapons, you will find that you cannot switch back to your original weapon -- this is because it longer exists.
Campaign
The No Weapon glitch is more difficult in Halo: Combat Evolved's Campaign. It involves overloading the map with objects, such as weapons, Grenades, and bodies, so that objects on the map start behaving erratically. Overloading is easiest on the Xbox version in Co-op; simply kill your teammate over and over until their corpses accumulate. With a little luck, you will de-load your weapons. You can also de-load enemies' weapons using this same method.
Observations
If, in Multiplayer, you observe a client who has no weapon, they will assume the animation for having no weapon, like in the first Campaign level, Pillar of Autumn.
However, if you observe a host who has no weapon, they will look very different. The host assumes a phantom weapon stance. They are actually still holding their weapon, but you cannot see it. If they were holding, say, a sniper rifle when they lost their weapon, then their arms will look like they are holding a sniper rifle. They can still shoot and melee with their weapon, and if they switch weapons, you will see a weapon floating in the air where they switched. They can also switch out their "phantomed" weapon for other weapons, changing how they hold their hands in the air.
Halo 2
Multiplayer
In Halo 2, the glitch requires an Oddball and a Plasma Pistol. Find an Oddball, and charge your Plasma Pistol. Walk over the Oddball and pick it up while still charging the Plasma Pistol. If you did it properly, your weapon will have been deleted -- your hands will be empty, and no reticule will be present on your HUD. If you come into contact with any weapon, you will automatically pick it up.
Campaign
In addition this can be done in campaign. I would suggest Outskirts because the Blind skull can be grabbed on any difficulty or regret because the Assassins skull is always there;it just doesn't work on Heroic or lower. First do the glitch where you hold three of the same weapon with the plasma pistol. Drop your duel wielded one. Switch between your weapons to be sure that you have two plasma pistols. Then go to the level's skull. Do the trick as mentioned above but with both plasma pistols. You should now be holding no weapons, but with the abundance of weapons in campaign it will be very difficult to avoid weapons on the ground so I would carry the level's skull with you so you can redo the glitch.
Observations
This can be used for some fun gametypes if everyone cooperates or can be used for making machinima. Please note, however, that unarmed players using the Spartan II player model can still throw grenades while Elites can't; this is because Elites don't have an animation for performing this action when unarmed.
Halo 3
This glitch can be achieved in Halo 3 as well. It mainly occurs during Custom Games, but it occasionally happens in Matchmaking, often during Capture The Flag battles.
