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This quote is being said by a mother to her child. She is explaining why she is acting differently or might be in a bad mood. PMS stands for premenstrual syndrome, which is a combination of symptoms that usually happen in women a few days before their period. Pissed-at-men Syndrome is another way to say PMS that is humorous but not necessarily accurate. The mother is saying that her child should have a better understanding of the situation because they are no longer a little kid.