Mariah Carey -- My Gimp Arm ... IS FABULOUS

This is painful ... Mariah Carey was so self-conscious about wearing a sling on stage this weekend in NYC, she tried to disguise her broken wing with ridiculous fashion accessories -- but it completely backfired.

Mariah -- who dislocated her shoulder while filming a music video earlier this month -- performed at the MLB All-Star Charity Concert Saturday night in 3 different outfits ... which included 3 matching sling disguises, including a weird superhero feather arm, and something that resembled a giant Q-tip.

The problem ... rather than divert attention away from her injury, the disguises made it way more obvious.