Somebody that does something annoying and makes u hate them for no apparent reason. Such as a weird face or a particular catch phrase. Some people might think the "wazzzaaaa" thing from scary movie is "uy."
(e.g. #2) "Uy, roaches freak me out!"
(e.g. #3) "You expect me to go on that roller coaster? Uy, no! You must be outta your mind!"