Everyone has seen it: a seething comment following an article on a popular website or a passive-aggressive tweet bashing a company. While it's tempting to respond with your own two cents in the heat of the moment, resist doing so, says Evan Carmichael, founder of EvanCarmichael .com, an information resource for businesses that covers such topics as reputation management, entrepreneurial advice and business strategy. "Start by understanding that no matter how hard you might try, you can't fully monitor or control these comments," he says. "But you can join in them." Here are three pieces of advice to follow when responding to a negative comment.