How to say in "work terms" that you're on your period?

Just say "  I'm on the "RAG"

Just tell them it's your time of the month. That's a respectable euphemism.

just say your having womens problems - if your boss is a man he wont want to hear any more and will give you a day or so off, but if your boss is a women she will probably just tell you to cope with it

Aunt Flo/Auntie Flow

Time of the month

On the rag

Red tide/army

Code Red

Monthly visitor

Lady time

Surfing the crimson wave/tide

Bloody Mary

The blob

Shark week

Having the painters in

The most popular terms in the world are:

There are communists in the funhouse – Denmark

The English have landed – France

Mad cow disease – Finland

Granny’s stuck in traffic – South Africa

I’m with Chico – Brazil

Little sister has come – China

The cranberry woman is coming – Germany

Birthing a blood diamond – no known origin, but brilliant nonetheless

You could say that you are having 'lady issues' or 'female problems'  usually one of those statements covers all the bases.

Using the phrase "female issues" will usually suffice.