The pigs really live up to their name when it comes to selfishness in George Orwell's novel, Animal Farm. Napoleon completely allows the power to go to his head once Snowball is out of the way. He demands that the other animals address him as "our Leader, Comrade Napoleon" and requires the other animals to step aside when he passes. He moves into the house and sleeps in the best bed. He acquires a taste for hard liquor and begins spending the farm's money on whiskey--for the pigs. He allows the hardest-working and most heroic of the animals, Boxer, to be sold for use as glue. He allows the animals to starve while he fattens himself on sugar, milk and excessive food.
Chapter 9 watches the tragic death of Boxer. Readers assume by the end of the chapter, that Napoleon made a great deal of money on the sale of Boxer's material worth as at the same time, a wooden crate presumably filled with whiskey arrived.
Napoleon also selfishly wanted to watch the improvement of his own race(oooo... I mean species). Thus he made other animals move to make way for the pigs, build the pigs a school, and work so that the pigs could have food, enough to make them fat.
Finally, a last example of selfishness is the repeated changing of commandments to suit the needs, rather the vices of the pigs.
I would say that just about anything that Napoleon does could be an example of selfishness. Napoleon wants all the power for himself and he wants all the material comforts to be for him and for the pigs.
So, for example, only the pigs were allowed to have any of the milk that came from the cows. Another example would be how only Napoleon is allowed to have sugar.
I suppose that you could also say that much of what Mollie does is motivated by selfishness. She does not work very hard and is always trying to get pretty things for herself.