sitting on pins and needles

To be sitting on pins and needles means that you are anxiously waiting for something to happen or for someone to show up at a certain time or place. Usually you are very anxious or nervous because what you are waiting for happens to be something which is also nerve-wracking once it arrives. It is often a difficult thing to be impatient about something which will be unpleasant which is why it feels like you are sitting on pins and needles.