what a fascinating lot of information!! coming from Dublin myself, the term going for a jar, means going to the pub for a pint (of beer ).Even if you end up drinking whiskey or Godforbid Whiskey and coke!!! you are still going for a jar! If you look up any old books or talk to any old folk, the reason it is called a jar, is because years and yonks ago they didnt use glass. The beer (of whatever sort ) was served in a ceramic mug.In England they serve Cider in similar mugs. There you go. As many have pointed out, to order what you want to drink, you plainly ask for it............a glass of Smythicks, a pint of Guinness, etc etc etc. Have fun Brigie