The drastic selfishness of Abigail is demonstrated by her willingness to cause people to die so that she can 1) avoid punishment for her own actions (dancing in the woods; drinking blood; etc.) and 2) essentially sentence Elizabeth Proctor to death in an attempt to rekindle her affair with John Proctor.
Placing her own needs ahead of those of the community is the basic definition of Abigail's selfishness. Accusing Elizabeth in an elaborate ruse to steal Elizabeth's husband and, effectively, kill Elizabeth is the extremity of Abigail's selfishness.
In accusing Elizabeth, Abigail shows a great amount of confidence (false confidence), believing that with Elizabeth out of the way Proctor will return to her (Abigail) with affection.
Her confidence is also evidenced by her initial play to deflect attention from what the girls have been caught doing in the woods. Mary Warren suggests that the girls simply confess to avoid extreme punishment. Abigail rejects this idea in favor of what becomes an involved hoax, destroying the life of the community of Salem.
Faced with a confession from Mary Warren in court, Abigail again shows her confidence and boldness when she concocts an act to threaten Mary Warren. She pretends to be harassed by Mary Warren's spirit and leads the other girls to follow suit. In this way, she dominates the situation and overwhelms the meek Mary Warren.
Abigail is selfish in the fact that she want John to herself and is willing to do anything to have him (she is mentally unstable and obsessed). Abigail shows confidence in the way she is able to control the other girls and how easily she lies. She is confident that John will leave Elizabeth to be with her. hope this helps! :)