A: Where have you been? I've been twiddling my thumbs, waiting for you to arrive.

B: Sorry that I kept you waiting. I ran into an elderly relative on my way here and had to be polite and chatted with her for a while. Otherwise, she will call my parents to complain.

Note: This idiom means “to have nothing to do, feeling bored.” Literally, it means to twirl one’s thumbs idly around each other, which is obviously something people do without realizing it when they feel bored. “Twiddle,” similar to “fiddle,” means “to turn about or play with lightly or idly.”