"I hate going to weddings with my girlfriend because once the band starts playing, she wants me to dance with her, and I've got two left feet."
You don't believe what you're being told. (If someone is "pulling your leg," they are joking with you or telling you a tall tale. So if someone is telling you something you don't believe - even if what they're saying might be the truth -, you would tell them to pull the other leg.)Pull the other leg
"You have the winning lottery ticket? Sure. Pull the other leg."
You have absolutely no excuse or no defense whatsoever.Yoy dont have a leg to stand on
"I know you said that you were at the library that night, but the security cameras at the No-Tell Motel filmed you checking in with another woman. Once your wife's lawyer finds out about this, you won't have a leg to stand on."