(Jeremiah 3:3 [KJV]) Therefore the showers have been withholden, and there hath been no latter rain; and thou hadst a whore’s forehead, thou refusedst to be ashamed.
Having a whores forehead is someone that refuses to be ashamed even when he or she clearly should be according to God.
(Proverbs 30:20 [KJV]) Such is the way of an adulterous woman; she eateth, and wipeth her mouth, and saith, I have done no wickedness.
Its basically also as the adulterous woman in proverbs 30:20.
How should we deal with someone that has a whore’s forehead?
Deal with them as with an unbeleiver.