A person who is addicted to repeating stupid acts on an ongoing basis. No matter what the outcome is they still continue to do it. Similar to an alcoholic.
That guy is a retardaholic, he keeps touching the electric fence.
2.) NOT someone who has a mental disability or is born with medically subnormal intelligence. People who fit this description are known as "special," "challenged," or "Earth angel."
That guy who goes around insulting everyone who is different from him is a real retard.
That woman with the mental handicap is an Earth angel. I'm glad I know her.