nolunteer

n. someone who doesn't want to do something or chooses not to do something others choose to do. the opposite of a volunteer or v. the act of choosing not to do something ; to opt-out of something.

roots in the latin nolo - to not want to, as opposed to the word volunteer, which originates from volo - to want to.

Jenny is a nolunteer. She nolunteered to participate in that extra-credit assignment.