red flag

Any signal that something is amiss. For example, if something funny showed up in your accounting, the IRS might say that a red flag has been put on your file, or more simply, that your account had been flagged. This term probably migrated from flags used in various sports to indicate a violation, along with the American cultural meaning of the word red.

If the golf course you're playing is of championship quality, you will probably see three different colored flags on the greens. Normally, you'll see six of each.

The red flag normally indicates that the pin is cut on the front portion of the green. A white flag is often used to indicate that the pin is in the middle portion, and a blue flag is often used to indicate that the pin is in the back.

Your eye can be wrong when judging the position of the pin from over 100 yards out, thus the use of these flags. When setting the course up for play, the position of the tees used that particular day will usually determine the position of the pins on the greens.

"I'm getting a C in biology."
"Haha, you're an idiot."
"I'll kick your ass."
"Uh oh, red flag!"

I guess it makes one realize just how common a device this in in conversation, at least among hormonally driven teenagers. It's also a somewhat embittered shot at a system that now thinks everyone in this country is liable to fly off the handle just because they threatened to kick someone's ass. Lighten up, America.