Cats do show fear. There are cats who love to be in the center of a room of people. However, equally as common are cats who cannot tolerate this much activity. They need to disappear. Whether this a genetic trait or due to insufficient socialization is open to debate. There is plenty of evidence linking insufficient handling of kittens between 3-9 weeks of age resulting in "skittish" cats. Aggression in these cats occurs when they have little choice but to use aggression to stop a threat (real or perceived). The key is understanding this a avoiding situations in which people pursue cats who are fearful. Dilated eyes, tucked tail, hair standing up and retreating is a cat who does not want to be there. Give him space!!
It is very difficult to socialize an adult cat. Gradually exposing the cat to the offending fear inducing stimulus while rewarding him for calm behavior is how it is done. The key is using a very palatable reward and only use it when the cat is disinterested in the fear inducing threat.DO NOT USE PUNISHMENT IN ANY SHAPE OR FORM! This will result in a heightening of the aggression.