I almost posted this the "That time of the month?" thread, but I was worried I'd cause a ruckus.
Anyways, the old "That time of the month?" question is why I always get so annoyed when women announce "Oh, ignore me, I have PMS" or "I must have had a PMS moment". It just leads men to think that any time a woman dares to have a strong emotion or opinion, she must be on her period, and as such, can be ignored.