Repost, because it's THAT important!
"Build those crits into interesting narratives. By optimizing for fun this way, a critical success may translate to a player doing enough damage to stylishly decapitate an enemy Kill Bill style, where a critical failure may mean a character draws their sword, only to realize they accidentally cut their belt in doing so, leaving their character pantless and having to roleplay with that both during the combat as well as after the instance has wrapped up. A dreaded outcome for a character doesn't have to be a dreaded outcome for the player, provided that the outcome is fun enough." -Teri, @GeekandSundry
What are some hilarious ways that you as a Gm have achieved this for players/past GMs have achieved this for you?