The episode was directed by Rob Oliver and was written by Joel H. Cohen and Jeff Westbrook from a story by Al Jean.
At the Springfield Retirement Castle after telling him a war story and pranking him with it, Grampa gives Bart a dud grenade.
Bart takes it to a school assembly and pranks them the same way Grampa did, scaring everyone away while ambulances and firefighters are called.
Ned Flanders throws himself on top of the bomb to sacrifice himself to save the school and Bart is forced to reveal the prank.
It’s a truly lousy episode because it fairly rings with indifference, glib cruelty, and enough lamp-shading of creative exhaustion to serve as platonic ideal for late-run ‘is that show still on?’ disposability”.
[1] Actor Nancy Cartwright was nominated for a Primetime Emmy Award for Outstanding Character Voice-Over Performance at the 72nd Primetime Creative Arts Emmy Awards as Bart Simpson, Nelson, Ralph, and Todd for this episode.