Demi Lovato is becoming a much more dangerous person -- she just earned her blue belt in Brazilian Jiu-Jitsu ... after training her ass off for the past year.
The blue belt is one level above white belt -- and 3 levels away from being a black belt.
Glazer -- who owns the gym -- flew back to town specifically to present Lovato with the new belt and tweeted, "I'm more proud of the work [Demi] puts in with nobody watching than i am what she does with the world watching."
Most blue belts usually train for about 2 years before moving up to the next level, purple belt.
It's been a helluva past few days for Demi -- from belting out the national anthem for the Mayweather/McGregor fight to performing for the VMAs ... and now this.
With great power ...