Where does the phrase flag it come from, as in
Oh, flag it, it's not working, I'm going to bed.
Where does the phrase flag it come from, as in
Oh, flag it, it's not working, I'm going to bed.
It is not a common euphemism as dockery suggests (at least, not on the United Kingdom, where I have never heard or read it used in that way). It may have been derived from "flag it" as an instruction to send a semaphore message between ships (using flags, before radio came into use). Hence it came to mean make someone aware of something. Contemporary use is to notify something, as in flagging an email by marking it in some way for attention.
When you are searching for any small item cannot or should not be moved, it is common to mark it in some way.
Consider a document that has several places that require signatures. The person preparing the document will put adhesive markers next to each blank. This practice is so common that you can purchase markers pre-printed with words "Sign Here".
Such markers are almost universally called "flags", presumably from the small brightly colored flags used as markers in golf, surveying, and construction.
The verb for applying a flag is "to flag".
Many data systems (including virtually every email system) have a feature for either drawing an administrator's attention or your own (in the future) to a particular data-item, and that feature is by obvious skeumorphism called and even depicted as, a flag.
Marking an problem for later work, even only mentally, can be called flagging by further extension.
No connection with flag in the sense of "lessen" (from Old Norse flaka, "to flicker") and not a minced oath for "fuck it".