You know those really flexible people that can twist their arms, thumbs, back etc. really crazy? They have a genetic defect that makes their joints and ligaments really soft and flexible.
Ultra-flexible people think it's cool and funny when they're young, but as soon as they're middle-aged they will get random sprains, dislocations, and permanent injuries just from walking or standing up.
They will live their whole second half of their lives terrified of their own body.