Uh oh ... Aaron Carter has been frightening friends and family recently with his threats and unhinged behavior -- most terrifying, his sister Angel's claim that Aaron threatened brother Nick's unborn child!

Two weeks ago Nick Carter Tweeted, "In light of Aaron’s increasingly alarming behavior and his recent confessions that he harbors thoughts and intentions of killing my pregnant wife and unborn child, we were left with no choice but to take every measure possible to protect ourselves and our family. We love our brother and truly hope he gets the proper treatment he needs before any harm comes to himself or anyone else.” He then added the hashtags #mentalhealth #GunControlNow and #GunControl." Aaron then surrendered two rifles to authorities.

Now Carter's putting a very visual expression of his pain on display -- the singer inked half his face with a HUGE Medusa and captioned a pic of the new look, "I’M THE BIGGEST THING IN MUSIC RIGHT NOW. I CANT BE DENIED. FACT CHECK ME." Uh ... check him into rehab!