A really long and complicated word used by kids to sound smart, when in all reality, very few people know what it means. Let's break it down:
anti - against, negative (anti-matter)
dis - un, anti, or not (displeased)
establishment - They way things are because the big guys say so ( "down with the establishment man!")
arianism - suffix to turn a word into a person that does something, or has a certain set of beliefs. (vegetarianism is a healthy alternative diet)
So, an antidisestablishmentarian is someone against those who are against the establishment. In all, it a rather redundant, pointless word.
antidisestablishmentarianism is a really stupid word.