a more colorful way of calling someone a 'hot mess', itself a way of calling someone a mess. The added color of 'tranny' and 'hot' takes the edge off of calling someone directly a 'mess'. It can have a range of connotation, from negative to neutral. Sometimes, ironically, it can be a compliment.
Alone, tranny is used as a greeting among gay men.
Gay#1: Heeey tranny.
Gay#2: HAAAY tranny!
Gay#1: Tranny, you are a hot tranny mess today; what'd you do last night?