Disjointed isn’t when you can bend your thumb all the way backwards — that’s double-jointed. Disjointed means "unorganized" or "disconnected."
Disjointed is an adjective that describes something as disconnected, illogical, or just messed up. A disjointed argument is an argument that doesn’t make a lot of sense. The same can be said for a disjointed sentence or a disjointed speech. In a medical sense, disjointed means "dislocated," or “separated at the joint.” When someone gets injured, they may end up with a disjointed shoulder or a disjointed hip.