A mode of awesomeness; A pure blank state of mind, in which you become greater (more beastly) than anything else that stands before you.
Also used when Kicking ass at black ops and someone tries to talk to you, but instead of giving them an actual convo, you just tell them "I'm in Beast-Mode right now, GET OFF MY NUTS"
When someone is constantly "Beastifying" they are in "Beast-Mode"
Bob: Dude, Jack has been in Beast-Mode for like 3 straight weeks
Will: I know, He has a 215 killstreak