AAA is what fanboys use to brag about game when they can't use the sales to brag about that game. It's a buzzword, it doesn't mean anything. You say that when you don't have anything to say to obscure the argument.
Also, if we go by the metacritics definition, we have that:
AAA: 90+
AA: 80-89.9
A : 70-79.9
B: 60-69.9
C: 50-59.9
D: 40-49.9
E: 30-39.9
F: 0-29.9
and that is just ridiculous.