I don't know if this is little, but I freaking hate mechanics who royally screw things up.
A little background: I have always done my own work on my own car. The exception to this is the time I did not live near my father. I lack a decent and complete set of tools (I have some, but never what I need) and while I was living in apartments, the rules forbid me from working on my car anyway. While I lived in North Dakota, I needed new brakes. I was forced to take the car to a shop and have a "real" mechanic do the work.
So, my irritation for today: I had to change the front brake pads. I jack up the car, pull the front tires off and attempt to remove the lower caliper bolts. I say attempt, because it was a mission. You see, that "real" mechanic had cross threaded the stupid bolts, utterly destroying them. Replacement bolts 11 bucks each and must be special ordered, as they're not a part that any of the stores around here carry regularly. My father rigged the bolts so I wouldn't be completely without transportation, but the warning is "don't go anywhere rescuing you would be inconvenient. Yea, sure. Maybe I'll just stay home all week.