We came in to grab a couple of beers after a walk....

We came in to grab a couple of beers after a walk. Once our waiter realized that we weren't going to order food her mood completely changed. Once we received the beers, we asked for the receipt. However when we received it we noticed she charged us one extra beer. Once we told her she said " oh I was waiting for you to leave". There wasn't a sorry or anything. I understand that the bill was small, however it doesn't mean we would've given her a small tip.