Plumbers who fail to show up on the day they suggested and then do not even respond to texts/phone calls! 
All the freakin' time!! We've been waiting 10 weeks now for someone to have a look at our Rayburn, because the back boiler is leaking. We can't relight it in the meantime, and the kitchen is starting to get cold, especially at night. Plus, I really miss the warming oven.
We've asked 3 times, when are they going to come. And all we get is, 'oh, well, we haven't got anyone going to the south end this week. Maybe next week.' Really?? So what you're saying is, you don't think our job is worth your time.
I've tried phoning other plumbers as well, but no one ever phones back.
In fact, I'm pretty steamed up now, so I'm marching right down to their office to sort this out. BostonDiner, if you want to PM me the phone number, I'll sort yours out, too! :p