An obese person, or one coming close to obesity. They are gross, smelly, unwashed and generally describe everything as delicious. Nothing disgusts an eatty, except a food shortage.
They can be found in foodcourts, or the nearest chair as any amount of exercise for them is an effort.
Within normal weight range girl: "Woah, check out that lard arse out the front of Macca's!"
Healthy sized guy: "What an eatty".