doing
something subjectively meaningless, i.e.
something that is objectively useful to everyone, including yourself, except the person who uses this phrase on you, who defines your activity as
useless and subjective only to themselves).
mother: Adam, go help your father in the yard, if I may interrupt you. All you've been doing to day in playing
Minecraft.
Adam: okay, I'll go help
dad, but remember that the purpose, of playing
Minecraft, I mean the actual game, is subjectively meaningless to youm, since everybody objectively defines it as useful except for you. (Adam goes off to help his dad).