To challenge the ruling on the field, i.e. call someone out on something that you believe is bullshit.

Derived from the NFL practice of coaches throwing a red flag to request further review of a play and give the network a chance to show 2 more minutes of commercials.
person 1 - My bad on not helping you out, I was working all day yesterday...

person 2 - I'll throw a red flag on that, you told me three days ago that you don't work weekends...

person 1 - Well, yea but...nevermind...
by JJ3672 December 10, 2008
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