If you are cock-a-hoop, you are very pleased and excited — often because of something you have just done well, not only because luck landed on you. A team that has won, a child with full marks, a cook whose cake actually rose: they can all be cock-a-hoop. It is cheerful, a little loud in feeling, and rather British; it also sounds a bit old-fashioned, so you will hear it more from older British speakers than from young Americans, who would more often say thrilled, over the moon, or on cloud nine. It is not a rude word, even though it starts with cock. The tidy idea is “delighted with a success”; in real talk it can also shade into “a bit too pleased with yourself”, depending on the speaker’s smile.