I relate to most of these mentioned so far.
A few more/repeats:
-Servers who walk into the kitchen during the peak of summer when it is hot as hell on the line, and say, "Jeez, it's soooo hot in here!! I don't know how you guys do it!!" STFU. Yes, we know it's hot, dumbass, we are doing a 10 hour shift next to the grill or the flattie or the wood burning oven. Get out of my kitchen.
-Servers who complain in the kitchen about paying taxes on tips, or tipping out to their bussers, runners, expo, etc. "I'm only going to walk with $250 tonight. This sucks!" STFU.
-In catering, when the captain doesn't count the tables correctly, or has an incorrect guest count, or an incorrect breakdown count (tallies of chix/steak/fish/vegetarian, etc).
-In catering, when guests have replied via response card and indicated vegetarian meal, but then see the steak plate and change their order when it is placed in front of them. "Oh, that looks good, can I have the steak instead?" or "No, I didn't order vegetarian. I want steak." Oh, really, because if your name is John Smith and you're sitting in the right seat with your name card John Smith, you ordered the vegetarian meal, John Smith.
-In catering, when guests show up to the event and demand a vegan/gluten free/dairy free meal, without having mentioned it to their host.
-Servers who are unable to take the right food to the right table.
-Cooks who think they don't need to learn how we do things in our kitchen.
-Cooks who don't use salt and pepper because they forget, or there's none on their station, or whatever weak excuse they have.
-Cooks who don't put any effort into family meal.