What is the plural of "sir"? [closed]

A security guard wishes to address multiple people respectfully at once. Does he say:

Sorry, sir, but this ID is invalid.

or

Sorry, sirs, but your IDs are invalid.

or something like

Sorry, gentlemen, but your IDs are invalid.

Solution 1:

Sirs is the technically correct plural of "sir."

That said, it is rarely used today. Gentlemen is normally substituted.

Messrs. (pronounced MEZ-erz) is, curiously enough, the technically correct plural of "Mr." (pronounced MIST-er) and also hardly ever used, except in writing.

Solution 2:

You don't need a plural so much as you need a vocative.
Sir is often used in the vocative, but not Sirs.
The correct vocative for more than one adult male (you can fudge on the "adult" part if you need to) is Gentlemen.

As in
Gentlemen, start your engines!
and
Sorry, gentlemen, your IDs are invalid.