'Trash Fire' reminded me a little of 'Tusk'. Very different films (both of which I happened to love), but with one common similarity at the centre of them - the characters have some actual depth to them. The first half of 'Trash Fire' I couldn't work where exactly the horror tag IMDb had attached to it was coming from. It seemed purely like a relationship-drama and a character-study of sorts. What I didn't realise was that all of that was purely character development and set-up, something almost unheard of in your average horror movie.
Even after completing the movie, using the term horror might be stretching things a little. There are certainly particular scenes that would fit right into a horror movie, but I think the whole thing is intended more as a very dark comedy/drama. In fact, very dark indeed. I liked it a lot though. Each and every one of the characters was fascinating in its own way. Almost all of the dialogue is excellently written and quite thought-provoking. The acting was also immensely impressive from the entire cast. I went in with low expectations and was treated to a nice surprise.