The rapper posted a wild video showing himself screaming in pure joy from within his car ... touting the idea that his 18-year-old, Tootie Raww, was supposedly cleared by a DNA test as NOT being the father to a baby that his GF/would-be baby mama allegedly claimed was his.

Check it out ... his victory lap is hilariously on-brand for Boosie. He's shouting from the top of his lungs and praising Jesus that the baby isn't his ... son's.

Boosie claims Tootie's SO brought somebody else's kid down to his high school graduation recently and sprung it on him like he was the father -- and Boosie thinks it was all BS ... even going on to call it a "conspiracy." Unclear if he's joking or not ... seems to be though.

Tootie appears to have taken ownership ... he was posing for photos with the child. But, his dad was skeptical from the beginning -- saying he didn't think this was Tootie's baby.

Boosie has also posted a ton of alleged receipts that he believes clear this up even further, throwing up photos of the supposed "real" mom and dad ... saying it's further evidence.