What does it "tell you" about a person when they sarcastically (or straight out) hurl insults at others?

What it tells me is that person is hurting badly and mistakenly believes that lashing out will make them feel better. People who result to sarcasm are often unheard and inconsidered and are used to being ignored. They are trying to push ons and get some kind of attention...even if it is negative, because they are so desperate to be seen and heard.