It refers to when you look at a person and they look so good it makes you sick, used esp. for females/drag queens/transexual females checking out other females/drag queens/transexual females - but meant completely as an admiration (with a slight connotation of politically acceptable jealousy)
This refers to somthing that is fabulous, over the top, fierce, the "T", eating it, flawless, frieghtening, nervous talent, etc. All terms coveted by the GBLTQ communities describing something that is extremely pleasing.
Mrs. thing was wearing the most sickening gown I had ever seen. She was just fierce!