Steelers William Gay -- 1-Man Shirtless Dance Party (video)

Steelers cornerback William Gay is taking that whole "dance like no one is watching" thing to new levels ... doing a shirtless dance revue on Instagram ... and we got to say ... dude's got the moves.

Gay -- for reasons we're not sure of -- posted five different videos to the 'gram of him (quite expertly) executing every hot dance move out there including The Whip, The Jook, and the death-defying Bobble Walk.

He even got in a couple of real life inspired joints, including Rich Homie Quan's signature onstage waddle, and his teammate Antonio Brown's touchdown dance The Beanie Wiggle.