It's only insensitive and nothing else when someone tells another to "get a life".
I often am told to "grow up" and that my obsession with cartoons and kids shows is "unhealthy" and that I "need to get a life". And I always give the same argument. This conversation happened just this week, and I definitely think I won. The person respectfully backed down and we continued our day on better terms.
This person had begun this argument after seeing me wearing my "Seddie" shirt, the newest one I made in anticipation for iLost My Mind coming out. They proceeded to ask me what it meant, and then laughed as I was telling them about the new episode