When does a prank become a dirty trick?

[hedgehog]

Examples:

Having pregnant women holding up signs with the slogan "Nixon's the one!"

Ordering pizzas sent to opponent's headquarters

Running a push poll - Would it change your view of candidate X if you knew he boiled kittens alive?

Sending out campaign literature with phony endorsements - Osama Bin Laden supports candidate X?

It seems the first example is a classic prank, while the others fall into the category of dirty trick. The first one is obviously a dig at the opponent while the others all cause fiscal damage or damage to the reputation.

[raccoon]

1. #2 causes more damage to the pizza parlors' bottom lines.

The last 2 are unarguably sleaze developed to the ultimate.

I have yet to see one frigging political ad on TV that isn't just negative campaigning, slamming the candidate of the other party.

[Dob Bole]

2. If you intend to cause harm, it's not a prank.

Pranks are done for fun. Dirty tricks are done out of vice, and that's the difference.