When it starts shaking and its nasal breathing turns rough, it's a sure sign of anger. However, since this happens instantly, there is no time to flee.
(From Bulbapedia )
Mankey is a primate Pokémon, similar to a New World monkey. It is a bipedal Pokémon with a round body covered in whitish, shaggy fur. Its nose similar to a pig’s snout, and it has red eyes and triangular ears with brown insides. Mankey's hands, two-toed feet, and the tip of its curved, prehensile tail are brown.
Mankey specializes in physical fighting, and is very aggressive and short-tempered. When angry, Mankey begins shaking and its breathing turns rough. Its rage peaks quickly, preventing its victim from being able to flee.
Very short-tempered and prone to going berserk when enraged. Signs that it is angry include shaking and rough breathing. However, at this stage it is already too late to flee.
Mankey lives in treetop colonies, and if one becomes enraged, the whole colony rampages for no reason.
Mankey is the third canonical Pokémon in the Tandor PokéDex (Fourth if you include Gyarados seperately from Magikarp, and fifth including Mega Gyarados). However, it has a new stage of evolution in Pokemon Uranium.
Considering its pig-like nose, long tail, and overall personality, Mankey have much in common with baboons.
Mankey may be a combination of the words man and monkey. It is also a possible pun on manky, which means inferior, dirty or worthless. Alternatively, it may be a combination of the words mad and monkey, due to Mankey's contrary and aggressive personality.