To do something in a way that (though it may not be at all necessary) is incredibly awesome.
To choose what is awesome over what is 'right'.
1) Dude 1: "hey man you want an apple or an orange?"
Dude 2: *Eats own head*
Dude 1: "OMG, you just totally stole an attack walrus"
2) Dude 1: "My GF just dumped me I'm going to set off a tonne of nuclear warheads whilst sitting in a bunker ontop of them and blast myself out of the atmosphere"
Dude 2: "Hey man, don't steal an attack walrus"
To do what is awesome over what is right. Usually unrelated to the previous activity. Originates from the webcomic 'Rock, Paper, Cynic', 2009-08-21.
1st Guy: Dude, if you don't go into work today you'll get fired!
2nd Guy: You know what would rock? Blowing up a pile of guitars!
1st Guy: Dude, don't Steal An Attack Walrus...
To do something completely unnecessary yet totally awesome, even if it's a bit more difficult than the alternative..
I didn't need to escape the enemy base on a rocket while it exploded in the background. One of the numerous cars would have worked fine. But at some point we all must choose between what is right and what is awesome. At some point we all must choose to steal an attack walrus.