So in the past few years since Lance Armstrong has popularized the Tour de France and bicycling in the US, there's been an upsurge in number of bicyclists on the roads for fun. This is cool, great for fitness, etc... But when you and two or three of your friends go for a ride and block the road 4 abreast, this is not cool!
Like the title says, my parents taught me when I was little that you ride your bike on the side of the road so you don't get hit by a car. Lately I've been seeing more people who go out and buy a USPS-branded racing shirt, and instantly believe they're in the Tour de France, and can ride anywhere they want to.
This is fine if it actually IS a race, with officials, proper warning signs, etc, but when you're cruising down the middle of a 45mph road doing 15mph around a blind corner, it's a safety hazard!
The worst part of it is, many have a snarky "Share the Road" mentality, which again is fine, but I expect anything in the middle of the road to be moving within the legal 15mph difference from the posted speed limit. This includes cars, trucks, scooters, motorcycles or even segways!