Update: I realized a little too late that I had constrained this story to 100 words (drabble length) for no reason, and had thus lost the whole point of why I had written the story in the first place. Here's what I originally intended to write in 237 words.
“Frizzum, frazzum!” the old man said.
His oldest two grandchildren laughed.
The youngest suggested a replacement.
“That’s too much,” he said.
They assured him it wasn’t, but he didn’t relent his uproarious pseudo-swears.
The weekend was long. His grandkids didn’t even know they were naughty.
On Sunday, they persuaded him to try a video game. It was an FPS. He had a slowly growing revelation: This game trained children. He had been sent to Earth to recruit soldiers.
He could use this. He played for a little while longer and then let the children have their game back.
When they left, he went to the store and bought the game and the machine to run it on. The kid at the register convinced him to buy a headset and a subscription to the Internet service.
It took him forty-five minutes to connect the infernal thing to his television.
He created an account and logged into the highest ranked game he could get into.
Strings of swears and other wickednesses from little children poured from the speakers.
He muted his microphone and swore.
Soldiers were known for their foul mouths, but the things they were saying about each others mothers would put enemies on the battlefield into a lethal rage!
His fifty years of assimilating himself into Earth culture had been a complete waste.
Well, he would show those idiotic ruffians what a polite, civilized person could do.