Jesus, you guys don't know anything about breasts.
D is actually on the average to small side. Incorrect sizing guidelines have led people to believe it's big, but what you think of as a D is actually more like an F or FF. That said, most women don't realize this either, so almost everyone thinks they're a different size than they are and even women think D is huge.
A true band size of 34 is also on the stocky side. 28 is quite skinny, 30 is slim, 32 is average.