Wiktionary
pull the other leg
vb. (context idiomatic English) (non-gloss definition: In imperative/precative form, used to imply that the speaker does not accept or believe what another has just said.)
Usage examples of "pull the other leg".
All I had to do was stick a leg in, wiggle my rump onto the sill, and pull the other leg in, and I had broken and entered.