Off Like a Shot

"Beep-beep! Zip-BANG!"

—Kid watching a Road-Runner cartoon (in a Road-Runner cartoon)

Any character who is about to dash off on a high-speed run inevitably, takes—just for a moment—a pose that looks like they're winding up for a pitch in a baseball game: one leg raised, the other bent slightly, the body twisted at the waist away from the direction of travel, with arms raised and bent at the elbows and often canted at an angle. Although their entire upper body is turned away from the direction they'll be running in, their head is always facing that way.

This posture is held for a moment, just long enough to be seen, and then the character is off and running, accompanied by a sound not unlike that of a ricocheting bullet.

Note that, depending on the level of "cartooniness," this can even be extended to vehicles, which will bend into an S-shape to mimic this behavior before taking off.

Examples of Off Like a Shot include:

Anime and Manga

Mashiro responds to an opportunity to mock Arika in episode 5 of Mai-Otome by running off in a classic Off Like a Shot.

Film

The title hero of The Mask often gets going with that kind of gesture. Furthermore, it was referenced in a little comic scene of Clark Kent in Lois and Clark getting dressed and leaving the same way, complete with the same self compliment, "Smokin'!"
Averted in Iron Man, in which he takes off and lands in the Mark II armor in a fairly stupid pose. This is fixed for the Mark III.
The Landlady in Kung Fu Hustle
Neo in The Matrix Reloaded does a version of this before he starts flying.

Live Action TV

This was one of Jackie Gleason's trademark shticks, accompanied with the Catch Phrase "And away we go!". Often led to a pratfall of some kind.
Christopher Reeve almost did this when he appeared on The Muppet Show, leaving Veterinarian's Hospital "Faster than a speeding bullet"

Video Games

Con Smith in Killer7 takes exactly this pose when he activates his extra-speed power.
Some depictions of Sonic the Hedgehog use this.

Western Animation

Most any Hanna-Barbera cartoon. Snagglepuss always used this pose to deliver his Catch Phrase ("Exit, stage left!").
Parodied in Freakazoid! by the titular character ending the stance by running at normal speed with hands extended in a superhero-in-flight pose and voicing a 'whoosh' sound. The parody is furthered whenever Freakazoid proves he really can move with super speed. There is little regard given as to why he does the first or how he does the second.
- Because it's funny.
Wile E Coyote chasing the Roadrunner tends to start off this way in Looney Tunes.
This is done quite often in Chip 'n Dale Rescue Rangers, most often by but not limited to the two chipmunks.
Animaniacs, particularly when the Warners ran from Ralph.
- In the first video game, you had to press a button twice to dash; the first press would get you in this position.
In My Little Pony Friendship Is Magic Fluttershy, of all ponies, strikes this pose just before attempting to catch up to a brainwashed Rainbow Dash in the second half of the two-parter "The Return of Harmony."