Comes from Starfox 64. A character would command fox to do a barrel roll in order to prevent being shot to deadness.

A barrel roll is when a fighter pilot makes his ship turn over, very quickly, in mid-air. It makes the wings harder to hit.

It's more common practice to shout this phrase at friends while they play video games. Especially if they can't do anything roll-like. The purpose is to be obnoxious, and quote old video games. Two of most peoples' favorite things.
"Son of a white boy, my Sim will not stop crying!"
"Quick, do a barrel roll!"
by Cap'n Awesome August 12, 2006
In Star Fox, you hit a Z or R button twice to barrel roll, which in turns, gives you a temp shield from lasers.

Also a fad saying for LUE
(Press Z or R twice.)

LUEer1: so I failed at life today
Random LUEer: Should of done a barrel roll
by dot dot dot January 30, 2004
A defensive maneuver you can get Google to do for you by searching for "do a barrel roll" without quotes.

An homage to Starfox 64.
Mike: "Hmmm... Let me type 'do a barrel roll' into google"

waits a second

Mike: "HOLY SHIT!!!!!!!!!1111"
by Dat Peppy Hare November 3, 2011
A word some gamers say when they are at a loss for words or don't know what else to say. This phrase originated from star fox, but has been so overused it has no meaning.
Me: Hi Chris.
Chris: Hi!
Me: I failed the math test. :(
Chris: Do a barrel roll!
by ShadowForce December 9, 2013
The controversial quote Optimus Prime is going to say in the upcomming Transformers Live Action Movie. The quote was submitted into the "Make Prime Speak" Contest and is currently by far, holding first place (Thanks to the YTMND Community) among a myriad of other crappy submitted quotes.
Some Flying Transformer Dude: OH NOES!!! I'M UNDER HEAVY FIRE!!!

Optimus Prime: Do a barrel Roll! lol
by SamuraiSilhouette October 22, 2006