If you want your Halloween chills a couple of weeks early, check out the video of Bush smiling and giggling as he raises the idea of World War III with Iran.
If you know you've decided to attack, I suppose it's funny, at least to a certain type of mentality.
There's no magic bullet reason for doing this - a similar rat's nest of reasons, I would think, to those for attacking Iraq. Finding it fun and exciting is certainly one of the reasons.
For another, consider how the media will play it, and how the Democrats will react, if the Iranians take any violent counter-measures, be they in the U.S., in Iraq, or elsewhere. The Administration can only win from ratcheting up the tensions, having "America under attack," etcetera.