Jake Paul Raps About S.I. Cover, Jutta Leerdam, $16 Million Mansion In New Video

Jake Paul just released the ultimate flex on his haters ... dropping a rap video bragging about his massive wealth and success -- and he recorded the whole thing during Nate Diaz fight week!!

The Problem Child shared the visuals for his new track, "Witness," on Friday ... and he put his luxurious toys, boxing career and love life on full display.

The 3-minute project includes footage from fight week and highlights from his win over Diaz -- and as it turns out, Jake even recorded himself mouthing the words to the song inside the ring after the match.

While Jake raps early in the track that he's "been tryna keep it humble for y'all," ... the lyrics are anything but -- with the internet superstar-turned-boxer listing all his favorite toys: private jets, Ferrari GTB and SF90, rare watches, and, of course, his $16 million crib in Puerto Rico.

Jake also mentions his recent milestones -- becoming a Sports Illustrated cover athlete, getting his own documentary on Netflix, as well as the Paul brothers being worth a billion bucks combined.

As for his fighting, the 7-1 pugilist spits about working harder than ever and still being hungry for more, despite all his achievements ... and how Cleveland couldn't handle his vision.

Paul even shows off his girlfriend, Dutch speed skater Jutta Leerdam, in the vid ... saying, "Gon' marry the queen of the Netherlands" as he holds her hand.