If you do something with your tail up, you are happy and confident when you do it. We'll go to court with our tails up. Note: People sometimes vary this expression, for example by saying that someone has their tail up or that something puts their tail up. They have their tails up being ahead of us in the league. There was no doubt that Mary Rand's outstanding performance on the first day put everybody's tails up. Note: Dogs often raise their tails and wag them when they are happy or excited.