An affectionate term for a rat, most usually domesticated. It has no relation to the general use of the word 'ratty' which describes a disheveled appearance.
"Aww!" Julie adoringly exclaimed as her friend's fancy rat affectionately kissed her hand, "your ratty is so cute!"
IHTM is an initialism for It Happened to Me. It is most commonly used by someone discussing a serious issue that he or she has come face to face with.
IHTM: My Father Committed Suicide