When someone is in "decent" shape while unofficially seeing someone and once the relationship becomes official they gain a shit ton of weight. The other person is then trapped in this new relationship with the newly fat fatty.
Omg did you see how Mikah fat-trapped Sarah into that relationship. The most brutal fat-trapping I have ever seen. Once they started dating he gained 70lbs!!
by Mappsofcambridge September 10, 2016
A Fat Trap is when you're on a social networking website, and see a good looking profile picture. Upon going to their profile picture, you see other photos of the person, and realize they are incredibly fat, and are actually ugly.
Person 1: Dude, check out this hot chick's profile picture!
Person 2: That is definitely a fat trap dude, look at her other pictures
Person 1: *checks pictures* oh god...thanks man, you saved me.
Person 2: That is definitely a fat trap dude, look at her other pictures
Person 1: *checks pictures* oh god...thanks man, you saved me.
by theoneandonly06 November 2, 2009
by Craig Cummings October 6, 2005