Someone who is fat, a name given to hungry people.
C'mon tuby stop eating the chicken and lets get some clean clothes for you?
A tuby is someone who blatantly fails at almost everything. Most of the time fat and if you were to compete with them at something they will be an easy adversary almost ensuring victory. (also a fat pink thing that dies very easily in the game defender for my htc inspire)
Dude i seen the biggest tuby in McDonalds yesterday.