The rule of cool is defined by TV Tropes Wiki thusly:
The limit of the willing suspension of disbelief for a given element is directly proportional to its degree of coolness. Stated another way, all but the most pedantic of viewers will forgive liberties with reality so long as the result is wicked sweet and/or awesome. This applies to the audience in general, as there will naturally be a different threshold for each individual in the group.