If You Saw Someone With Pants Unzipped....

[Captain_Awesome]

@Quasimodem

In my younger days, we used to say “xyz”, meaning “check your zipper”, although I don’t know how “x” came to mean a check-mark?

Wouldn’t YKK make more sense?

@Quasimodem

“Flies”, plural, in the UK?

Yes. ‘Flying low’ is perhaps the most widely heard euphemism I’ve encountered in the UK. Whether I use it depends entirely on the situation.