From the Italian "Questo cazzo" abbreviated to "sto cazzo" in southern Italy, in many dialects it translates to "stu cazzu", very often shortened to "stucazz".
Literally it means "this dick", obviously referring to "my dick".
It is more or less a swearing way to say "yeah right", so it can be used in various scenarios
Someone that busts ass at everything (Ex: school, running, being a good kid, driving, girls, LIFE). Stuvasses are extremely cocky. Always careful to drink in moderation and planing snack breaks between drinks, Stuvass tries to stay in controll of all situations(esp. situations involving girls). They are also Sore Loosers, viewing everything in life as a contest that Needs to be won at all costs.
Antonym: Appletop
"Being a Stuvass, i plan on busting ass the first mile to get a good start, busting ass the second mile because it is mostly down hill, and busting ass the last mile for a strong finish."
A person who isn't accepted by the majority of the people around him. Makes unfunny jokes, says irrelevant things, says weird shit. Overall a person who doesn't make sense.
dumbass: yo what did the dog say to the other dog?
normal person: what?
dumbass: bark bark i like bones.
normal person: stupass