“The human race has only one really effective weapon and that is laughter.”
- Mark Twain
“Wit is a dangerous weapon, even to the possessor, if he knows not how to use it discreetly”
- Michael de Montaigne
It basically means that we weren't brought into this world to be sad. "Laughter Is Our Only Weapon" means that laughter is what is gonna bring joy and a happy spirit back. Laughter will cut through someone trying to bully you. If you just laugh and stay happy. Your weapon has done it's job and so have you.