Mainly in the US, a stupid or annoying person.
[From the offensive term retard, a noun formed from (mentally) retarded.]
The term in this combining form that has appeared most in printed sources, and which is best known outside the United States, is celebutard (from celebrity), a person of no particular intellectual accomplishments who is best known for being famous. However, the most common creation is the deeply offensive fucktard, a despicably stupid person. A debutard (from debutante) is a stupid upper-class or rich person. An e-tard (see e-1) may either be a person who has overused the recreational drug ecstasy or one who is unable to cope with modern technology, especially computers and the Internet.
Many other examples have appeared fleetingly online, such as lame-tard (an intensification of the slang term lame in the sense of socially inept), scientard (from scientist) a person deeply immersed in research or study who is likewise perceived as lacking social skills. It has appeared in politically motivated insults, such as conservatard and libtard (in the UK, with an initial capital letter, it refers specifically to a supporter of the Liberal Democrat party).
The financial and popular success of James Cameron’s film Avatar (2009), about a classic colonial encounter between exploiters of mineral wealth and noble savage indigenes on a distant world, led to the press and bloggers sarcastically naming its loyal supporters Avatards, even the ones who didn’t paint their faces blue.