To ‘twiddle your thumbs’ is to rotate your thumbs around each other while your hands are together. When you say you are ‘twiddling your thumbs’ it means you are idle or do not have anything useful to do. If someone accuses you of ‘twiddling your thumbs’ they mean to say that you are not working hard or doing anything of importance. This is a casual idiom used more often in social contexts.

1. Don't just sit there and twiddle your thumbs when I'm doing all the painting.
2. She just twiddled her thumbs all day when there was so much cleaning to do around the shop.

1. A successful business is always innovating and planning for the future. You can't sit there and twiddle your thumbs while the competition gets the edge.
2. I find this role so unchallenging. I tend to finish my tasks early and spend the rest of the day twiddling my thumbs and looking for something to do.