To “spend a penny” is a polite euphemism for going to the toilet.

The phrase goes back to Victorian public toilets, which required users to insert a single penny in order to operate the lock.

Although it sounds crude, the phrase is actually considered a polite way of announcing that you are going to visit the bathroom. Historically, only women would announce they were going to “spend a penny,” as only women’s public toilets required a penny to lock. Men’s urinals were free of charge.

“I’m going to spend a penny.”