TAN is an acronym for "Touched a nerve". If you ever offend or
hurt someone you are said to have 'touched a nerve' with them or TAN'
ed them. It derives from the use of the word by the
character Michelle in an episode of BBC
2's comedy sitcom, The Royle Family after she offended her hosts. Also, to make known to someone who has offended or upset you, you would exclaim, "TAN!"
Conversely, if you wish to gain forgiveness or repent for any TAN you have caused, you simply ask by saying 'NAT'.