Food was good, beer is mediocre. I was sitting at ...

Food was good, beer is mediocre. I was sitting at the bar having a pint and some food. After finishing my food, I needed to use the restroom so I put a coaster over my beer, the international sign for "I'm not done with this one, yet". After coming back from the restroom, my beer was gone and they said it was because they thought I bailed without paying; mind you I had an open tab, so it's not like I am the type of person to pull a fast one. The bartender then poured me a half pint, or to the point where he thought they dumped my beer. After being made to feel like I was the person who wronged them and apologized, they scoffed at the apology and made me feel unwelcomed after a clear misunderstanding on their part.