From another thread about Rory Mac's scary face:
Mine:
My favorite stares of all times in no particular order:
Fedor: I am about to either pick some vegetables or turn my opponent into one
Wanderlei: The immenent violence coming your way is going to be bloody and spectacular
Carlos Condit (old style WEC scary face, he has calmed down): I am very upset because I think you were the guy who picked on me because I was skinny in grade school, and I have to look like this so I don't cry. (love his fights and him in general!)
Conor McGregor's Weigh-in Screams: So gaunt from the weight cut and so black are his eyes, you can see the back of his skull and the weight of his self belief when he screams that pre-victory victoriousness pronouncement.
Rory MacDonald: The closest thing to a mass murderer in the sport, and thank heavens he found mma and did not kill half of the population of his native BC.
Guida vs. Diego, in cage. 
CerronePoundsOnMeStrong - Guida vs. Diego, in cage.
Oh yeah! That was epic and both of those guys have great stare downs, especially Diego. He looks like he is going to bite his gumshield in half!
Cain jds 3 during the intros. I thought they might start when buffer was still in the cage 