Any
word which does not express a clear
meaning or a
distinction among
phenomena in the
real world, but rather serves to express
anger,
rage,
condemnation, or
indignation towards the
person or
thing described.
Human beings use
snarl words not to clearly
communicate statements of fact, but rather to make it clear that they are
pissed off -- or to get you
pissed off along with them.
Sometime social commentator Robert Anton Wilson has pointed out that it is impossible to have a conversation about the politics of censorship with a person who keeps using the word "smut", or a discussion of racial issues with a person who keeps saying "nigger". His point is not that such words should be banned, but that the language of piss-off-itude is not conducive to reasonable discourse.
A word may become a snarl word not through its original denotation, but through its use to stereotype, accuse, or attack. For instance, "communist", "fascist", and "anarchist" are words with perfectly viable dictionary definitions. However, they are much more often used to slur people who do not fit these definitions, than used to refer to people who actually fit those categories.