your ass is itchy

When you want to let someone know that you think they are full of shit; or they are wrong and/ or lying

Person 1: “My girlfriends a model. My mom loves her! She’s so sweet & beautiful!
Person 2: “No way! When has your mom met her? When have you met her? you always talk about her but none of us have ever met her. You haven’t even met her! We’ve all only seen the same picture again & again.

Person 1: “no, we met um, ah, last month’” “ she’s just always out of state since, you know, she’s a model”
Person 2: haha dude, no way! Quit lying! Your ass is itchy!