Uninterested or Disinterested?

Disinterested

Disinterested means not taking sides or impartial. It is usually used to describe a person with no personal benefit at stake.

We are struggling to identify twelve disinterested people for the jury.
(We are struggling to identify twelve disinterested people.)
An investigation into the penalty decision has reportedly uncovered that the referee was not disinterested in the outcome of the match.
(The referee had a personal interest in one particular side winning.)
Most of the spectators at the football match were disinterested.
(This is only correct if the writer means that most of the spectators did not support one side or the other. The match may have been very interesting.)

Uninterested means not interested. It is the consequence of something being uninteresting (i.e., boring or uneventful).