Somebody who devotes their life to one specific activity because they have absolutely nothing
better to do in their spare time. One such example is somebody who plays
video games more than 12 hours a day because they have nothing
better to do. No activity is exempt from this though, and video games can't be singled out, this applies to sports, outdoor activities, etc...
no_lifer: You have no life. All you do is play video games.
other_
guy: No, I have other things I can do. I just choose to play video games.
no_lifer: Well what about me. All I have to do with my life is play football? I'm not a no lifer. I have
friends.
other_guy: Actually, you don't have a life. Just having
friends and spending your time playing sports doesn't mean you automatically have a life.