Allow me to impart a bit of wisdom:
It is my understanding that when you use this phrase, you are implying that the said 'lifeless' person is wasting their time, and should engage in activities that better resemble the actions of society as a whole- IE: going downtown to drink, going to clubs to dance and drink, go to the movies, play a sport, etc - OR [and this is probably more likely] that they should engage in activities that you opt to participate in.
I'm sorry to inform you that your own personal life is not the measuring stick for every other human being alive.
Different people choose to spend their lives different ways. Some people like to get up early and meet their friends for breakfast. Some like to build shit and watch sports. Some like to go downtown and get plastered. Some like to go to clubs. Some people just like to sit at home and chill out. Everyone's unique (I would have thought that was obvious). When a person spends their time doing things they enjoy - they have a life. Life is spending your time on things you enjoy. No one really gives a fuck what you think about how other people spend their time. No one cares how you spend
your time.
So from now on, when you feel compelled to tell someone to get a life, do everyone a favor and just shut the fuck up.