I think that for me, the thing that annoys me most is when you get a family group coming into a cafe and just making such a massive unnecessary faff out of the entire experience, and somehow managing to dominate the entire space with their endless fussing and dithering. For example, four adults, four kids and a baby come in, stand around everyone's way for a bit saying 'Oh, are there enough tables? I'm not sure there are. Perhaps we could push two together. Perhaps Ophelia could sit on your lap? Oh wait, are these people going? Yes, wait a minute, Toby, we're going to sit down soon and then Daddy will take you to the toilet - Guy! Guy! Can you grab that table and perhaps ask the waitress to clear it so we can push these two together? Right, now, Ophelia, you sit here and Jago, do you want to sit here with Toby or - OK, Toby, well, perhaps if you ask Mummy nicely she might swap chairs with you so you can have the one with the blue cushion... Jago! Jago, take your coat off please, darling? Would you like Daddy to get your gilet out of the backpack, if you're cold? Guy! Can you find Jago's gilet for him please?"
This goes on at top volume for about 20 solid minutes while every member of the party, adults and children, moves seats about four times, then there is a 20-minute debate about what everyone would like to eat with endless negotiations and questions, then one of the adults goes up to the counter to order and then calls loudly over their shoulder to the other people at the table for clarification on every single thing while a massive queue builds up.
"Right, so, could we get three flat white coffees, please - wait a moment - Izzy? Did you want decaf, darling? Ok - so, two ordinary and one decaf, then - sorry, wait a second - GUY? GUY? Did you say you wanted tea? Oh he's taken Jago to the toilet, has he? Ophelia, did Daddy want tea, do you know? And what cakes do you have please? Right, OK - children? They've got blueberry muffins, lemon drizzle, Victoria sponge and chocolate brownie, which do you all want? What's that Toby? I don't know if the brownie will be like the one you had at Oliver's party, no, I expect it will be quite similar - well, no, darling, I don't they do have any Bakewell tart but I'm sure you'd like the muffin, although they're quite large... Ophelia, are you sure that's what you want because I don't think you'll be able to finish it?"
[everyone in cafe loses the will to live and is shouting 'JUST FUCKING ORDER AND SIT DOWN' silently in their own heads]
These sorts of families are also a nightmare when checking in at airports or taking their seats on an intercity train. SO MUCH FUSS. SO MUCH NEEDLESS COMPLICATION. SO MUCH WET, CLUELESS DITHERING OVER NOTHING.