Woody Allen once said, "We're all our brother's keepers, but in my case I share that honor with the Prospect Park Zoo."

Bad neighbors are nothing to laugh about, according to the Appraisal Institute. An unkempt yard, close proximity to a sex offender, or having an unfortunate commercial facility nearby (like a power plant or funeral home), can reduce the value of surrounding homes by as much as 15%.

"The impact can vary tremendously depending on a few factors: how 'bad' the bad neighbor is, the kind of neighborhood you're located in, and the type of market that exists," says Carlos Gobel, director of residential services at Integra Realty Resources in Miami.

But what exactly is a "bad" neighbor? Definitions vary, but real estate professionals say it boils down to any home or business enterprise that turns people off.

"A bad neighbor is one that has no consideration for the rest of the community," says Mindy Pordes, co-founder of Pordes Residential Sales & Marketing in Aventura, Fla. "For example, someone who doesn't take care of the outside appearance of the home, such as the gardening, painting of the outside of the home, roof, garbage and general upkeep. In addition, a bad neighbor may have constant visitors taking up parking spaces, perhaps on the street, loud house parties, dogs that bark all night or stray cats lingering around."

A "bad" neighbor can also be a business or government enterprise whose very existence drives the value of your property down. Here, the seven suprising neighbors that can reduce your home's value:

So can you fight back against problem neighbors? In the case of a landfill, power plant or sex offender, your options are severely limited. As long as your neighbors are following the letter of the law, you'll just have to grin and bear it — or move. If not, you have every right to petition your local government authorities for a grievance and at least get the matter reviewed.

If it's a residential property causing the problem, however, you might have better options.

For starters, you can leave a polite letter left in the offending homeowner's mailbox to get his or her attention. In addition, Pordes says that if the home is located within a homeowners association or condo association, the association can send letters to the homeowner and deny the homeowner community privileges to try to ensure the homeowner complies with the community rules and maintains home values.

Most cities and towns do have ordinances against messy yards and junk-laden driveways, so check your community's rules and regulations to see what applies.

Unfortunately, many cities and towns also have landfills, power plants and other less-than desirable commercial-sized neighbors.

Most likely, you're just going to have to live with them.