My personal gripe is when people pile their plates with tons of stuff and then leave most of it.
That annoys me too, although I sometimes have taken something that looked tempting and didn't like it, so may I be excused for leaving it?
We did stay at a hotel where brekkie was about £35 (depending on exchange rate) but we got a 2 for 1 offer. However tempting it would be to eat our way through the menu (which included everything from Miso soup through lots of cooked items to delicious pastries, we just couldn't!
So it was fruit, yogurt, eggs, mushrooms and bacon and I confess that I took a Danish pastry for Ron. 