The Sharpest Tongue

Is usually honed by fear...

Most likely someone who treats other people with disrespect by being abrupt, sarcastic or rude and speaking as if everyone else is an idiot, is in fear of being discovered an idiot themselves. They live in constant angst of their insecurities being discovered and their actions are a defense mechanism to cover up how they really feel about themselves. Which is contrary to the external image and actually an internal hell, a trap they feel they can't get out of.

Generally they are to be avoided if possible, especially on a social level, because they inject nothing but negative energy into any situation and sap useful energy. Sometimes though, such as in work or other groups, they can't be avoided. It's important not to let them intimidate you and buy into their behavior. One approach is to pick one piece of their negative commentary that can be turned neutral or positive, and turning the conversation around to a more positive level to redirect them. Also consistently treating them in small, subtle ways with respect and reinforcement of their good traits, will signal to them that you're not "going to play."

In that manner you have avoided the counterproductive bombardment in an unavoidable situation, particularly if it's work where it's ongoing, and set the tone for future interaction on a higher plain. It also may open the door a crack for them to feel less trapped and possibly work their way out of their insecurities. This takes a lot work and reinforcement, especially since it's easy to unwittingly fall into the trap yourself.