What is the most strictly enforced unwritten rule of British pub etiquette that outsiders just don't seem to grasp?

Posted by Necessary_Angle2117@reddit | AskUK | View on Reddit | 250 comments

For me, it has to be the "invisible queue" at the bar. To a tourist, it just looks like a chaotic mob of people leaning on the sticky wood, but everyone in that huddle knows exactly who arrived before them and who is next.

​That, and the absolute mortal sin of waving your money or clicking your fingers to get the bartender's attention, instead of just waiting patiently and doing the subtle 'eyebrow raise and head nod'.

​Aside from the sacred, unbreakable laws of buying rounds, what is the absolute fastest way someone can out themselves as having zero pub etiquette?