One of my favorite characters in Season 1 of HBO's "Game of Thrones" was Syrio Forel, the "dance teacher" Eddard Stark hired to teach his daughter Arya to fight with a sword. The "Not today" meme has caught on a bit with "Game of Thrones" fans.
"Game of Thrones" Scene: "Not Today"
Here's the clip with Arya saying it below.