Bar staff – if your remember only one thing….
… especially the ‘claw’ – the (bad) habit of bar staff handing over pints of stout to waiting customers with a claw-like grip around the top of the glass instead of holding it by the bottom half of the glass.
“Remember” Padraig pointed out, “the bottom half of the glass is the barman’s, the top half is the customer’s”.
In like vein, bar staff succumbing to the (to be discouraged) practice of letting the countermount spout touch into the Guinness in a glass have sometimes been warned off by the disapproving customer with the imprecation, “Get your spout out of my stout!”.