The otherworldly ability to detect fatness in other people. See gaydar.
"Look how zoomed-in and blurred her Friendster photo is. My fatdar is going crazy."
by Hugs_not_drugs April 02, 2004
Similar to gaydar, but differs in the way that it allows you to detect a fatty before they have a chance to sit on and/or eat you.
Whoa! Look at that butterbeast. My fatdar is going crazy!
by JB April 02, 2004