A militant and/or unpleasant atheist who actively dedicates time in their life to ridiculing theists. Generally, they are marked by a lack of courtesy and deductive reasoning skills. Other traits include actively identifying themselves as atheists before anyone asks, frequent use of 666 in screen names as bait, and talking about religion more than religious folk.
After he studied his state representative's beliefs he decided to become an antiestablishmentarianist. My folks aren't happy that I am an antiestablishmentarianist.
Someone who becomes an atheist because something bad happened in their lives, so they immediately think that a higher power couldn't have possibly been so mean/ heartless/ evil, so they don't exist.
Frank: Oh noes! I lost my little toe in a thrasher! There's no way that someone up there could've been so cruel, so there must not be anything there!
Someone who is an angsty atheist. Generally belittles religious people as being superstitious sheep and believes themself, and their god of science, intellectualism, randomness, and meaninglessness to be superior to the illogical superstitions of the confused masses of ignorant religious people.