Manstration refers to a monthly hormonal cycle for men. Some men get cranky and bitchy for no reason regularly, just like what women go through in their monthlies (known as menstruation). This is where the term manstration comes from.

Manstration(男人月經)指男性每月經歷的荷爾蒙分泌周期。有些男性會周期性地表現出無端的煩躁、易怒，這種情緒變化跟女性在月經周期(英文為menstruation)的狀態類似。由此便誕生了manstration這個詞。

For example:

You are extremely unreasonable today, are you on your manstration?

你最近變得特別不可理喻，你是來“月經”了嗎?