Old and New Jokes

Late one Friday in Dublin, a policeman spotted a man driving very erratically. He pulled the man over and asked him if he had been drinking that evening.
Aye, so I have. Tis Friday, you know, so me and the lads stopped by the pub where I had six or seven pints. And then there was something called Happy Hour and they served these mar-gar-itos which are quite good. I had four or five o those. Then I had to drive me friend Mike home and o course I had to go in for a couple of Guinness — couldnt be rude, ye know. Then I stopped on the way home to get another bottle for later… And the man fumbled around in his coat until he located his bottle of whiskey, which he held up for inspection. The officer sighed, and said, Sir, Im afraid Ill need you to step out of the car and take a breathalyzer test.
Why? Dont ye believe me?