To pull someone's leg is to tease them by making them believe a joke. Stop pulling my leg, are you pulling my leg, he was pulling her leg.
In practice it appears with a real possessive rather than the word someone, so people say pulling my leg. To pull someone's leg is gentle by definition, since the joke has to be admitted.
1phrasepull someone's legTo tease someone by making them believe a joke.
“Uncle Joe likes to pull someone's leg at every family dinner.”
pull someone's leg is a teasing.
Also accepted in games: pull your leg
Originally Scottish, meaning to make a fool of somebody, perhaps from tripping them.
The phrase from Scotland originally meant to make a fool of someone, often by cheating him. One theory is that it is derived from tripping someone by yanking or pulling his leg in order to make him stumble and look foolish.
Etymology from Wiktionary, CC BY-SA
Practised in Idioms