As I ate my lunch I had time to mull this over. Why would a plain woman wear a slogan ostensibly uttered by someone particularly photogenic or of public interest? I have just checked to be sure, I believe it is called Irony.
I wondered who else would wear it?
A young attractive woman might fear appearing to be vain.
A young unattractive woman might fear bringing attention to her appearance.
An older attractive woman might fear looking silly if people were actually not impressed by her looks.
I wondered if this leaves the T-shirt as not ironic at all, as the wearer is the only person you would expect to wear it anyway?