First, you aggro a mob near an instance and bring it near the instance. Then, you pop bloodrage and wait until there is 1-2 seconds on the buff. When it reaches around 1 second, zone in quickly. You will stay in combat and gain 1 rage every 3-4 seconds until it reaches 100. Unfortunately, the glitch is gone once you zone out of the instance, use bloodrage again, or go into combat again. The only use of this bug seems to be to be able to stay with 100 rage for the first pull of the instance. Still, somewhat useful for those fights where the boss is at the front of the instace.. like Razorgore.
