Lady Gaga is being sued by famed R&B singer Teddy Riley, who claims she boldly aced him out of his contribution for the song, "Teeth."
According to the lawsuit, Riley produced the hit song back in 2009. He claims he was promised 25% of the writing fees but got zilch.
The song was featured on the album, "The Fame Monster" the same year -- it's Gaga's breakout work that turned her into a global star ... and Riley --who became famous in the 90s R&B group Blackstreet (remember No Diggity) -- feels betrayed.
He's suing for $500,000 and punitives ... which are designed to teach monsters a lesson.