Is "on one’s tippy toes" an idiom?
Yes, this is a figurative expression. It is often used to mean movement in a sneaky or quiet way. Billie Eilish has used "on your tippy toes" to describe the action of walking quietly on the balls of the feet, to reduce noise and lift your weight off the heels of your feet. Ex: She crept down the hall on her tippy toes. Ex: If you walk on your tippy toes, you can sneak up on someone.