Get a life!

"get a life" と言うフレーズは"Saturday Night Live"（これはコメディー番組ですがsitcomではありません。シカゴに駐在していた頃時々見ていましたがNHKのサラリーマンNEOのようなスタイルのコメディです。）でポピュラーになった台詞だそうです。
一寸長くなりますがWikipedia による解説を引用します。
Get a life is an American English idiom. Used as a command, the phrase generally instructs its addressee to go out and make their way in the world, without being supported by outside sources such as parents or benefactors. It may also be directed at someone who is perceived as boring or single-minded like geeks, to suggest they acquire some other, more practical interests or hobbies and get dates, find a job, move to their own house etc. It is also used when people don't know about something that another person considers popular or normal, such as a certain TV show or board game that this person assumes everyone else knows about.
The term was popularized by William Shatner's appearance in a 1987 episode of Saturday Night Live, in which he tells a group of trekkies to "get a life." However, evidence of the term's use in the vernacular extends at least back into the 1970s, perhaps as part of a mainstream backlash against hippies.
その後Get a Lifeと題されたsitcomも放送され益々この言葉が広まったそうです。
American Heritage Dictionary of Idioms には次ぎのような説明がありました。
Acquire some interests or relationships of one's own. For example, Stop sitting around and complaining. Get a life
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Standard way of suggesting that someone has succumbed to terminal geekdom. Often heard on Usenet, especially as a way of suggesting that the target is taking some obscure issue of theology too seriously. This exhortation was popularised by William Shatner on a "Saturday Night Live" episode in a speech that ended "Get a life! ", but some respondents believe it to have been in use before then. It was certainly in wide use among hackers for at least five years before achieving mainstream currency in early 1992.
NEET にピッタリの言葉のようですね。