"get a life" only means "I don't care" in the mind of the teller.

<SMART=ASS>
Sorry to be uber-pedantic (and contrarywise to the origi-poster) but "get a life" is telling someone to do something. With implications (and I infer that) of inferiority of their opines sic.
</SMART>

Isn't lexicography, semantics, etymology and communicativeness wonderous? (;-)