Yeah, it's kind of REALLY FUCKING ANNOYING when I hear this. Not even just directed at me. At anyone.
What would you consider a better activity, asshole?
Maybe watching TV? This site says that Americans spend 5 hours a day doing just that. Would that be a better use of my time? Or perhaps I should be texting my friends about unimportant shit. Maybe go to the football game and watch D-average people throw a ball around? OR... Go to a bar and get drunk! Yeah, that would be a MUCH better use of my time. Spend time chasing neurologically-deficient women for vapid, empty sex, drive to Wal-Mart to get cheap shit I don't need... There certainly are quite a few activities that I should be focusing on more.
So while you're off doing all of these things, leading an exciting, important life, if you could take the time to tell me that my hobby that makes me happy is pointless and wasteful, I would VERY MUCH appreciate it.