Justin and Hailey Bieber Hug, Butt Slap Around at Pool Table in Pennsylvania

Justin Bieber was playing pool Friday night, and he landed a shot in the back pocket -- Hailey Bieber's back pocket!!!

Justin and Hailey hit up the pool room at the Hotel Rock Lititz in Lititz, Pennsylvania, acting super goofy and romantic as they tried their hand on the felt.

They were hugging, dancing (sorta) and then JB smacks Hailey's butt as they erupt in laughter. You gotta listen to the woman who shot the video ... hilarious!

Justin and Hailey hung out for a couple hours as they chilled with a few friends ... under the watchful eye of hired muscle.

The buzz is that Justin's in town to record music with the Clair Brothers. It's interesting ... this is Amish Country, but it has musical roots. The rehearsal facility has seen the likes of Beyonce, BTS, Taylor Swift, U2, Elton John and Billy Joel. It's considered one of the greatest rehearsal spaces in the world.