Sarcasm has been used to insult me many times; usually to try and make me feel like an idiot. My enemy could instead choose to yell "Your an idiot!!" in my face. But that would expose the verbal assailant's feelings, which would in turn open the assailant up to public scrutiny. This is not what the assailant wants. It is quite possible that the sarcastic person is not aware of their anger with me and thus may not be at a point of bursting out in anger. Rather the sarcastic one is often a frothing mixture of various suppressed human emotions, including those of resentment for the potential victim.
So whether aware or not of their hatred for their victim, whether holding back tears of rage, or bumbling along unaware yet tensely ready to pounce, sarcasm is used to insult; and it is a back-handed cowardly weapon of the emotionally fragile. A choice made by wimps who can't meet their enemy in battle, and thus prefer to slip something in their drink. (By 'battle' here I mean anything from mortal combat to heated discussion).
But what do I mean with all these metaphors? I am saying that insulting sarcasm carries out its purpose in what I think is the most mean-spirited and pain inducing way: indirectly. By being indirect the assailant delivers an insult which unloads over time as a virus in the mind of the insultee. Sarcasm is hard to defend against initially because it is often not at all certain whether the insulter is being sarcastic or not. The comment "Ben, your a great singer!!" seems innocent enough. This ambiguity usually is enough to prevent the insulter from being identified by observers as belligerent or it at least gives observers an excuse to not intervene on the insultee's behalf. This excuse is the plausible deniability needed to allow a 3rd party observer to sit idly by during verbal abuse and still appear respectable among peers.
Thus the moment passes, no one has defended the insultee because of ambiguity, and the insulter has not been identified as a mean spirited for the same reason. Also the one being insulted may not even yet be aware of the insult. But assuming he/she has heard it, assuming the acid of hate has entered the intended mind, the real cataclysm is yet coming. Upon realization, the thoughts of the insultee go like this: "I was just insulted, everyone else thinks its OK, and the vile perpetrator is now grinning ear to ear because he will pay no price (because of a lack of conscience, or a simple non-awareness of his own actions) and it is now socially unacceptable for me to retaliate, because I was not directly attacked." This is when Satan laughs a great belly laugh, this is when a fairy somewhere dies, this is when the mental anguish begins. It is a uphill battle from here to address the insulted person; to address the problem with frank discussion. As is the case for myself, I fear, that the vast majority of the time the insult is pressed down into the insulted individuals froth of personal emotions, adding to future confusion, anger, and in all likelihood, retaliative sarcasm. The world sometimes seems very dark.
Here are a few definitions of sarcasm:
Answers.com : A cutting, often ironic remark intended to wound.
Wikipedia: Sarcasm is the rhetorical device of using a characterization of something or someone in order to express contempt.