[shardling]

The best definition I've seen for what constitutes a game is this: A game is an experience created by rules.

That captures what distinguishes a game (as an artform) from other media. You could throw in some qualifiers to perhaps narrow it down (is paying your taxes a a game?) but it's not really necessary.

[vacri]

A prison sentence is a game?

[shardling]

Like I said, you can try to narrow it down, but it's pretty hard to define a rigid line between art and not art in any medium.

Although your particular example is kind of amusing, given the prominent role of the Prisoner's Dilemma in discussing elementary game theory! :P