月經、月事的英文是"menstrual period"，不過是比較正式的說法。要提到女生「那個來」時，可以用that time of month（一個月中的那段時間），來形容。
看看老外聊天時怎麼用time of month：
A I asked Anne if she wants to join the beach trip this weekend but she refused.I am so hurt.
B It's that time of month again.We can change our schedule for her if she's coming.
A 我問安妮要不要加入周末的海邊行，結果被拒絕了。我好受傷。
B 因為她那個來。她要加入的話，我們可以改去別的地方啊。
time of month例句精選：
I think it's that time of the month.
我想這個月的生理期又到了。
My wife is crabby. It must be that time of the Month.
我的妻子心情煩躁，一定是到了來例假的日子。
She is really in bad temper in that time of the month.
她來例假的時候脾氣實在太壞了。
要跟別人提到月經這件事時。用此句話說出來，比較不害羞。
相關：Time for Vegas.是否該去透透氣了。
Time for Vegas.I finally finished this paper.
是否該去透透氣了。我終於完成論文了。
相關：time vampire花時間的東西
Facebook is a time vampire.I usually can do nothing after browsing on it.
臉書真的很花時間。通常玩完之後就沒時間做別的事了。