From Halopedia, the Halo wiki
In the Great Journey, when you're escorting Sergeant Johnson's Scarab in a Banshee, fly to the ground near the Control Room and wait for another Banshee to fly down to you, hijack it. The Brute pilot will fall out and land on the ground, but he will not die.
Fly down and get close to the Brute, and he will calmly walk toward you and follow you wherever you go. Even though he is making berserker yells, he will not attack you. If you do the same with others, they, too, will follow you—so you can have an entire pack of harmless Brutes follow you wherever you want. However, if you kill one of them, and another one sees you, he will go berserk and attack you.
Also, in the same area, when you see an overturned Wraith, get out of your Banshee. The Brute there will not attack nor have a weapon.
This glitch occurs because many brute pilots on the Great Journey are spawned without weapons. The brutes want to attack the player, but have no way of doing so, since they have no animations tied to meleeing with no weapons. This can be proven by the fact that weaponless brutes go berserk when you kill one of their pack. In addition, if you get a weaponless brute on top of a wraith you're piloting, he will board it and start hitting you.