Idk if its the fattest thing but it sure was memorable. One time back during a summer home from college I'd gotten off after a late shift at a job. I was craving some Steak N Shake but the local one was no longer 24hrs. Undaunted I drove 30min to the next nearest one to get my fix. I was pretty hungry so I ordered 2 frisco melts. Unfortunately I pulled the dumbass move of not checking the bag and got all the way back home before I realized they'd gotten my order wrong.

Hungry, and angry, both at the restaurant for fucking up my order and myself for not checking the bag I stormed all the way back over there to get the correct food before once again returning home to eat.