I'm not sure if this counts as horrible DM, but I do feel bad about it (I was the DM, actually, Story Teller in this case). This happened around this time last year. The oWoD anniversary edition line of books had come out, and I'd spent (what is to me) a small fortune getting everything needed to play a game. We'd run several one shots to warm up, and had one fun multi-session game. My players: my best friend, his wife, his step daughter (14), and two of my brothers (15 & 17).

Now, my brothers were only visiting for the summer, and this incident took place on the very last day that we could possibly have a game. For the game, with input from my players, I had come up with a one shot where they would play low generation Sabbat 'trouble shooters', working for the 'True Black Hand'. I'd cleared all clans, and gave them freebie points befitting elders. Sure, not original, but my players thought it would be fun. I'd planned several 'missions' that tied together, that we should have been able to play through at a fast pace. Then some things happened that destroyed my mood (I was really looking forward to one final game), and I threw a fit . I am not proud of it, and apologized later, but I probably qualified as a terrible ST at the time. Here's the long of it:

1. I'd gotten off work, raced home to grab my gaming materials and my siblings, got some snacks, and picked up Starbucks for all of my players. I arrived at my BF's house in record time... to discover that my BF and his family were not home. After some texting back and forth, I was informed that they had forgotten about the game (I have no idea how, as we'd been discussing it over the phone and in person all week) and would be back soon. It took them about an hour

2. When they got there, everyone just piddled around for another hour or so. I had to corral them into the dining room (largest table in the house) one-by-one. A small nit-pick, the table was filthy, and I was the only one working on cleaning it.

3. Several weeks prior, my BF's step daughter had knocked over a full glass of milk while we were playing a game. My friend's book and some character sheets were ruined. As a result we had all agreed on a rule: No liquids on the table, place your drinks on the floor (linoleum). Since I had cleaned the table, I knew that there were no threatening beverages present. I laid out the character sheets and assorted materials, then left the room to see what was keeping my friend from joining us (turned out he was fixing his mother in-law's printer). I'd only been gone a few minutes, when I hear shouting from the dining room. My friend's step daughter had knocked over her glass of soda, and it went all over the table. Luckily, only the materials which I had printed (character sheets, character creation guides, etc.) had been ruined, and she was frantically cleaning up. I was miffed at this, but kids screw up. Then the girl's mother stated that she'd known the glass was there, but decided against reminding her kid of the 'no liquids' rule... 'because'. WTF? That got me mad. Kids make mistakes and forget things, but parents should remind them when they do. At any rate, I swallowed my anger because they were cleaning things up.

4. I went back to help my friend with the printer (as we now needed it for new character sheets). This took a good 20 minutes. Finally everything is ready, and I head back to the dining room. Where I discovered that my BF's wife and her daughter had given up on cleaning. I noticed a trail of soda coming off the table and onto my chair... where my bag of books was sitting. I quickly checked the bag (made of cloth), and sure enough, it had absorbed a lot of fluid. That’s when I lost it. I told my brothers to pack up their stuff, and we left. On our way out, my BF’s wife starts yelling at me, saying it’s not a big deal, and it’s bull crap that I decided to leave because of an accident. I then spent the rest of my night cleaning and drying my books.
Later, after I calmed down, I explained to my friend that I don’t make very much money, and I tried to explain that replacing books which I should not have purchased in the first place (used my credit card) was a big deal for me. I also tried to explain that it was not the accident, but the failure to correct the accident that had damaged my books, and that’s what pissed me off.