Something flagrant is bad — so bad you can't ignore it. A flagrant foul in sports might send you to the bench, and a flagrant violation of the law might send you to the slammer.
The current meaning of the adjective flagrant — "obviously offensive or disgraceful" — is thought to derive from the Latin legal term in flagrante delicto, which literally meant "with fire still blazing" and is used figuratively to describe a situation in which the criminal is caught red handed. Aside from a flagrant abuse of the law, the word can also be used to describe anything that is obviously bad — like flagrant bad taste or flagrant abuse of the rules of grammar.