It means to tease someone by saying something shocking as a joke.
eg: She said she saw the plane's wing fall off, but I think she was just pulling my leg. I didn't really steal his wallet. I was just pulling your leg. Actually, I found it on the ground near his car. Note: Pull someone's leg的意思是说一些令对方惊讶的玩笑,并非中文扯后腿的意思。 例:她说她看见飞机的翅膀掉落了,我想她只是逗我玩儿的。