The leggings illusions is when a girl with no ass wears super tight leggings to make it seem as if she has ass when she doesn't. This makes the ass look big from a distance, and makes a man's mouth drool for dat booty. But when you get close or you get her home and taking them legging off, you realize that she has a small ass.
It's still sexy, but it's a lie.
Britney was so fine, she had a nice ass when I saw her walking around campus. Then I got her in my dorm, she took off the leggings, and I realize that she had a small ass.