As it has come to pass, a nerd is apparently a person who dislikes geeks and denounces them as little more than second-rate, wannabe nerds. Anyone who claims to be a nerd is automatically not a nerd (as anyone who claims to be of a particular label is automatically not). True nerds are essentially smart dorks who still look dorky. True geeks, on the other hand, are smark dorks who act but don't look dorky. Nerds are generally academic in a general sense. Geeks are typically tech-oriented. Most all people who outwardly claim to be nerds or geeks are just pseudo-intellectual kids or teenagers who wish they were smarter than they truly are. True nerds, and some true geeks, often have a "Clark Kent" or "Peter Parker" complex: they don't proclaim they're as such, but rather they wish to be normal and/or at least accepted as viable members of society. Very few true nerds and geeks actually exist in contemporary society.
Most of the people posting definitions here are not true nerds.