There's just no way you can possibly fold here. 99.99% of the time he's just got the 6, or possibly Q6. If the guy did have quads, then kudos to your friend for making a sick laydown. However, it's still a horrible laydown.
As far as the odds of flopping quads with a specific pocket pair:
In this situation you have 22. So to flop quads you need 1 random card and both of the remaining 2s.
(2 / 49) * (1 / 4
* (47 / 47) = 0.000850340136 EDIT: I did the math based on each possible flop permutation ( 2x2, 22x, x22) and it averages out to the same number as above.
