From a post on the straight dope:

I work in advertising, where frequently the challenge is to get the client to agree to pay you as much money as possible, then go away. The problem is that some clients (particularly new ones) will absolutely refuse to let an estimate pass their desk without making some alteration, just to show that they’re involved in the process. Now, if you go in with a carefully crafted ad campaign, where everything beautifully interlocks with everything else, then this moron blindly slashing away with his pen will inevitably cock it all up.

The solution is to give him a helicopter. A helicopter is something glaringly, obviously wrong, deliberately thrown in to satisfy a busybody’s need to “do something.”

It comes from a video producer I once knew who would always include an actual helicopter (for aerial shots of the city) in the estimate every new proposal he made. The helicopter was always obviously far more expensive than anything else on the list, and the client would always immediately cross it off before approving the proposal. End result: the producer got to do the project as he wanted, the manager got to feel useful, and everyone was happy.

An anti-helicopter is the opposite of this. It’s something you inadvertently put in which seems to make everyone fixate on it at the exclusion of what you were trying to show them. If you’ve been in enough debates or done enough blogging, you get a general sense of what the anti-helicopters are and yet it doesn’t stop you for occasionally throwing one out. You’ll be making this long, well structured, elaborate argument and add in a totally tangential sidenote and all of a sudden, everyone’s gone off in a huge 100 post argument about whether the sidenote is valid.

A proper understanding of helicopters and anti-helicopters can be very useful when trying to convince.