Blac Chyna's Booty Pop Is Full o' Poop

Blac Chyna and her big ass jumped into bed with an ass-enhancing product ... a lot of people think is just a fake ass scam.

Chyna posted an ad promoting Booty Pop, a spray that claims to be an "All Natural Booty Enhancer." The endorsement was fleeting ... she deleted the post almost immediately -- perhaps because the company is bombing with the Better Business Bureau.

Apex Vitality, which makes Booty Pop, gets a C from the BBB -- and a ton of reviewers don't even give it that much credit. We checked and some call it a straight-up rip-off. One person said she was grossly overcharged and wanted someone to "shut them down immediately because this is one big scam."

We made multiple calls to Apex Vitality, but got no response. Ditto for Chyna's camp.