Marilyn's Law
Any discussion regarding portrayals of female beauty in the media, especially in regards to weight and shape, will devolve into a discussion of Marilyn Monroe's dress size (what it was, whether it was a constant, what it would be in today's dress sizes, whether she presented a more realistic beauty ideal, etc.)
A: I can't believe how skinny models have gotten!
B: I know! I wish we lived back in the 1960s when people liked a woman with real curves.
A: Did you know Marilyn Monroe wore a size 12?
B: Can't we have a discussion about this without invoking Marilyn's Law? You know she had to diet and exercise and get plastic surgery, right? It's not like there were no unachievable standards of beauty for women and all was well with the world back then, either.