pull somebody’s leg

to full or trick somebody, to tell someone something that is not true for fun, as a joke:

„Did you really win the race or are you pulling my leg again?“

„Come on, of course he is not a professor of psychology in Boston. He was just pulling your leg, Meg.“

Stop pulling my leg – I don’t believe you made this cake yourself.“

pull somebody’s leg = dělat si z někoho legraci, věšet někomu bulíky na nos