-Do not exaggerate things when talking to a PMSing woman. She will see through your lies, and bash you for them.
-Do not make stupid jokes, or any jokes at all. She will take offense to them, and in turn, she will offend YOU.
-Do not tell a PMSing woman that she is wrong. A PMSing woman is never wrong.
-Do not tell a PMSing woman that she's "overreacting". If you do, she will overreact more than you can handle.
-Do agree with a PMSing woman, no matter what she says.
-Do agree and apologize when a PMSing woman tells you you're doing something wrong.
-Do only say purposeful things to a PMSing woman. Rambling will not get you brownie points.
-Do buy sweets for a PMSing woman.
-Do not take anything she says personally, but do what she says. It's for your own good.
Added thanks to Pablo: Do not talk to a PMSing woman about things that don't interest her.
Added thanks to Terra: Do not tell a PMSing women that her jeans are getting smaller.
