'End him rightly' is a swordfight tactic suggested by Gladiatoria, a medieval fighting manual. What it basically says is "If you want to END HIM RIGHTLY, unscrew your pommel of your sword and throw it at your opponent, then finish him with your sword." Due to ridiculousness of this tactic, it became a meme, and is often depicted as an ultimite strategy for a joke. Just google it and hopefully you'll get it.