Lay off a woman's size, Trump
Every man who has a sister, mother, wife, girlfriend or even a random female in their life who they've spent more than three minutes with knows that telling a woman they've gained weight is just never going to go down well.
Every man knows that, except, it seems, Donald Trump.
I don't subscribe to the theory that Mr Trump overwhelmingly lost the debate last night.
But he may well have lost it this morning. Mr Trump should sue his campaign for political malpractice. Why on earth was he allowed to go on morning TV and say former beauty pageant winner Alicia Machado had "gained a massive amount of weight. It was a real problem."
That, or, better, he should look in the mirror and have a long hard think about his obsession with the way women look.
No woman likes to be told her own weight is a problem and most women don't really like men telling other women that their weight is a problem either.
Weight is an intensely personal, sensitive and often tricky issue for women and it is something women talk about a lot among themselves, usually with empathy and support.
So we circle the wagons when a man talks disparagingly about a girlfriend's weight. "Miss Piggy" is about as bad as it gets.
I suspect Alicia Machado has a lot of new girlfriends this morning - because we've all been there.
Our own weight fluctuates. In stressful situations (a Miss Universe beauty pageant, for example) most of us tend to gain or lose a bit. It's normal. Having a man criticise us for doing so is not helpful.
If Mr Trump is serious about winning women voters, in the suburb of Philadelphia or the small towns of Ohio he should learn some basic gender etiquette.
Lay off our size.