If it were not true, the saying "revenge is sweet" wouldn't be so popular. There is no doubt that getting back at someone who has wronged you feels good—but, of course, there are degrees of vengeful acts, and there are consequences of those acts. "Revenge can be fantastic!," says Shannae Rickards, Ph.D., a psychologist in private practice in Thousand Oaks, California. "It's totally human to want to hit back when we are hurt. You see it in children. If a two-year-old pulls another child's hair, the other kid is going to turn around and do it back, maybe even…