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（男人月经）指男性每月经历的荷尔蒙分泌周期。有些男性会周期性地表现出无端的烦躁、易怒，这种情绪变化跟女性在月经周期（英文为menstruation）的状态类似。由此便诞生了manstration这个词。

For example:

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

你最近变得特别不可理喻，你是来“月经”了吗？