Someone who smells fear blood or hurt and just destroys there opponent recently at 132 we saw some sick killer instinct by Joe lauzon he always is impressive with that and a guy who's prolly my number 1 pick really living up to his nickname would be Carlos Condit. Who comes to mind when you guys think killer instinct? 
Natural born killa!
Wanderlei Silva and Fedor
Probably Vitor.
Probably Vitor.
BJ Penn
nick diaz, diego sanchez, matt serra,bone jones are examples..
but of all ??
i would have to say
Mark Kerr and Mustafa al Turk
Jose Aldo
Fedor, BJ, Anderson (when motivated, then again, you can say the same for BJ), Wanderlei, Barnett.
Choco Al
Lauzon is a good one.
FEDOR!!!
Penns instinct has always impressed me not because it's the most blood Thirsty but it's he always looks so calm then bam your fucked!
justin h darling
kid chaos - Jose Aldo
That's a scary man
Wanderlei Silva, Carlos Condit, Melvin Manhoef, Nick Diaz, Vovchanchyn, Fedor, Liddell, Aoki (yes, Aoki), Rousimar Palhares, Gomi, Kid Yamamoto, Imanari
Too many to list really
sandro, blanco, palhares,
WOW! Nobody has said Leben yet? Roger Huerta is another good name for this list.
Melvin guillard
GSP
Jim Miller