Referring to the first, yes it is derived from STFU which means "shut the fuck up" Stuff you is a tamer version more widely accepted, yet still holds the same message of shutting up.
dude: hey why dont you see me some time?
chick: stuff you and go away!
Derived from the term stfu.
KeWtLiLaNgELgUrL69: hey u sem kewl kan i add u to mah budilist??!/1
Regular Person: Stuff you.
Regular Person: ::blocks::