Grandma Time is quality time spent with your grandma. Everyone, even punk-ass metalheads, has at least one moment in their life that they can qualify as Grandma Time. It should never be interrupted, because Grandma Time lost cannot be recovered. Ever.
*John Lydon is walking through London with his grandma when fan walks up to the pair*
Fan-"Dude, omg, I am a HUGE fan of the Sex Pistols! Can I have your autograph!"
*Lydon pulls switchblade on fan*
Lydon-"Do NOT interrupt my Grandma Time!"
Lydon's grandma pulls out a butterfly knife and whispers-"Don't interrupt his Grandma Time..."