From daysoftheyear.com. According to them, they say…
"The bartender is everyone’s favourite person on a night out. They will keep you well supplied in beverages – probably of an alcoholic variety – at any bar or pub you happen to visit, as long as you have enough money and aren’t too drunk to be served!
World Bartender Day is the day to appreciate the staff in your local bar. They work hard to keep their customers happy and often don’t get paid very well!
Remember to always be friendly to the bartender, especially by being patient if you have to wait to be served.
Give the bartender a smile and say ‘please’ and ‘thank you’ – the bartender will appreciate it and you are more likely to get better service next time you buy a drink.
Most importantly, if you’re in a country where tipping is expected, make sure you tip appropriately!"