Most Helpful Guy
Big is a relative term. How a given cup size looks depends on the rest of your body. What would look well proportioned on one person might look too large or too small on another. Moreover, there is no common taste among either men or women as to what constitutes and ideal of body proportion.
Consider if you will this graphic:
This graphic shows sizing info for bras made by a major manufacturer (Haynes). This is off the rack, not custom sizing.
Take note that the cup sizes go up to size M.
If we were to call a C cup large, we would run out of superlatives before we got up to size M.
"I can never remember, is 'enormously large' bigger or smaller than 'stupendously large'?"
As it happens, my wife wore a J cup when we first met. Since then, she has lost some weight and is down to a G cup. This cup size looks totally proportional on her. As such, you'd never suspect that she's packing as much as she is.2