twiddle one's thumbs

twiddle one's thumbs {infml} (to do nothing for a period of time, usually while you are waiting for something to happen; to be idle ) — бездельничать, лодырничать, слоняться без дела; бить баклуши; ~ груши околачивать; в потолок плевать; дурью маяться (в знач. бездельничать)

Example 1: She has been twiddling her thumbs all year and is now unable to pass her courses at school. — Она весь год баклуши била (дурака валяла), а сейчас не может сдать зачет в школе.

Example 2: He'd better work than stand around here twiddling his thumbs. — Ему бы поработать, а не слоняться здесь без дела (не баклуши бить.)

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People often move their thumbs around each other with their fingers joined together, because they are bored or waiting for something.

Related vocabulary:
under [без дела]