Demonheart is the name of a song by power/fantasy metal artist Luca Turilli. To say that someone has a demonheart is to say that a person may seem amazing, but they will completely screw you over when you least expect it, typically in a horrible way.
Demonte is Smart, Funny, Athletic, and very faithful. Never will be a fake friend. Very freaky but doesn't show it in public. Very good at video games a clutch player and a fast learner. once you get to know Demonte he is one of the coolest people you'll ever meet.
Characteristics of someone with sinister thug like attitude. Down-to-earth dominance among friends, blunt with opinion/tell it like it is ( cuz they'll enjoy your humiliation or stupidity of something) can be a bully, maybe psychopath can definitely pull off this word phrase combination.