The Old Pink Dog Bar was the bar in Han Dold City that Ford Prefect was in when he discovered that his Guide had his full entry on Earth on it.
On the bar was a parrot, which recited the names and telephone numbers of local assassins. There was also a disembodied arm which helped the barman both in serving drinks and in threatening people. It had belonged to the original owner of the bar. When he died he bequeathed it to medical science, but they didn't like the look of it so gave it back to the bar.
It appeared in So Long, and Thanks for All the Fish and the Quandary Phase of the radio series.
The barman completely refused to take American Express cards as payment.