play footsie

play footsie with sb (flirt by secretly touching someone's feet under a table with your feet to show sexual interest in them {usu in continuous tenses} — заигрывать (касаясь ноги объекта под столом)

Example: Mark was playing footsie with his boss's wife (under the table) during the dinner. This is pretty dangerous!

Related vocabulary:
[hanky-panky]