A derogatory term used to call someone who is not only dim witted but ugly as well.
Person 1: You know I went out with her because I felt sorry for her being pig-ugly but I bet you didn't know that I used to do her homework as well 'cos she was so thick!
Person 2: Shit, so you mean she was a total ratfish then?
Person 1: Yeah.
the man of my dreams
ratfish is the only guy i'd fuck!