"Feel one's oats" is an idiomatic expression meaning to act with confidence, energy, and enthusiasm. It originated from the way horses behave when they are given oats - they become lively and full of spirit. Some synonyms for this phrase include being full of spunk, being in high spirits, feeling frisky, or feeling feisty. These phrases suggest a sense of excitement and vitality that comes from being full of energy and confidence. When someone "feels their oats," they are typically feeling good about themselves and their abilities, and are ready to take on the world with enthusiasm and determination.