Ok , maybe not rage quitting, but certainly a 'I quit because I am now combat ineffective, do not have the necessary fire power to effect the outcome, it's turn two and the game has now so frustrating, tiresome, and depressing that I will take any excuse to concede and walk away' quitter.
Some people call it bad form, but personally see no point in continuing a game if there's no way you can win or even come close to winning. If it's turn 2 or 3 and your combat ability has been eviscerated, why would you go on? Why wouldn't your opponent (who is now 7 to 1 for kill points) not end the game to be at least kind or even just considerate? To beat a dead horse? To keep going and see if he can get 10 kill points to 1 then tell your friends that you just 40k beat someone who was so below your skill level that you just wanted to see how far it could go?
What's your favorite 'I got so beat so bad, I quit by turn 2' story?