The festive season is when large numbers of people who scarcely go into a pub between January and November suddenly find themselves crossing the threshold and end up annoying both staff and regular customers by their total ignorance of the normal standards of pub etiquette. There’s an entertaining (if somewhat sweary) summary here. Another one I would add is standing about in large groups in the middle of the floor completely blocking movement around the place despite the fact there are plenty of seats available.
But, on the other hand, given the parlous state of the pub trade, perhaps it’s not a good idea to be quite so sniffy. After all, if the bar staff are polite and the other customers friendly, they might be tempted to come back at other times of the year rather than dismissing pubs as cliquey and unwelcoming. And it makes a refreshing change to see pubs actually busy – often with people drinking alcohol (!?) – and even finding it difficult to get a seat.