Nashville bar owner Joey DeGraw's not happy about Morgan Wallen's alleged rooftop bar antics, 'cause while the tossed chair didn't hit anyone ... it could still ding the city's booming nightlife scene.

Joey and his brother, singer-songwriter Gavin DeGraw, know all about Nashville's Broadway party scene -- they own one of the strip's hot spots -- and he tells TMZ ... he's annoyed Wallen allegedly chucked a chair from the 6th floor because it could've seriously hurt someone.

JD says he's not worried about Morgan and his drinking -- in fact, he thinks the incident might help his career -- but he is worried about how it might impact tourism on Broadway, Nashville's main attraction attraction.

The DeGraws' bar, Nashville Underground, is one block away from Chief's -- where Morgan was Sunday night -- so, the brothers have a vested interest in people coming to the area ... and feeling safe when they do.

To be clear, Joey says he didn't see the alleged incident, but says chucking furniture off a roof is, obviously, a dumb choice ... no matter what Morgan's circumstances turn out to have been.

He's preaching good bar etiquette, and whether you're a celeb or a normie, Joey says throwing a chair off a pal's roof just isn't polite -- referring to the fact Morgan is friends with Chief's owner, Eric Church.

Despite it all, Joey says Morgan's still welcome to check out Underground sometime ... though he jokes they might have security tail him to avoid any potential trouble.

As we reported ... cops arrested Morgan after they said he tossed the chair off the roof at Chief's. The really strange part is we got photos of him happily chatting up a young lady on the rooftop ... moments before the chair went flying.