Unknown. Possibly related to doylem (“a stupid person; an idiot”).
Meanings
Disdainful indication that something is obvious; see duh.
This sucks. I have no idea where I want to go to college, and Ms. Whitaker's making me decide right away. But how? There are so many colleges. How does anyone decide? / Easy. Pick the school with the best chick to dude ratio. Doy. 2018, Robia Rashid, Dennis Saldua, “The Smudging” (11:09 from the start), in Pam Thomas, director, Atypical, season 2, episode 7, spoken by Sam and Zahid (Keir Gilchrist and Nik Dodani), via Netflix:
—Wow, he looks pretty angry. —Doy!
Uh, doy! 2015 March 6, “Kimmy Has a Birthday!”, in Unbreakable Kimmy Schmidt, season 1, episode 9, spoken by Kimmy Schmidt (Ellie Kemper):
(Yorkshire, dialectal, endearing) A term of address to a young child.
Whear is thi' Daddy doy? Whear is thi' mam? / What are ta cryin for, poor little lamb? 1872, John Hartley, “A Hawpoth”, in Yorkshire Ditties: Second Series, Wakefield, West Yorkshire: William Nicholson & Sons, page 112:
[…] an' then as aw caught seet o'th' three little doys 'at wor crooidled up i'th' winder corner, tryin' to keep warm, ther little nooases lukkin like three half-ripe cherries wi' a drop o' dew glistenin' on 'em, aw thowt, better net just yet for their sake. 1886, “Sweep! oh! Sweep!”, in Yorkshire Tales: First Series, London: W. Nicholson and Sons, page 30: