As roadies, we avoid commuters at all costs. They are slow until you try to pass one, not particularly good bike handlers, and they think they own the road, bike path, sidewalk, or any other paved or unpaved thoroughfare they happen to be huffing and puffing down the center of. If you find yourself needing to pass a commuter, know that they will do everything in their capacity to pass you at some point later on. They won't smile or wave, but just smugly pedal by as if they were planning on riding 6mph, and then ramping it up to 30, and you just happened to be riding by as they did this. Once you let them pass you, they will inevitably tire and the process continues. Your only options are to exert some real modicum of effort to keep them from catching up, or turning off. You cannot ride slow enough to let them get away, because they will always ride slower.
Mountain bikers think they are cooler than we are, and they're right. They wear baggy clothes, smoke pot, drink beer, and get to ride over rocks and off cliffs. This requires skill, and courage, but generally not as much fitness as racing a road bike. This means that we see them as slackers that don't have to suffer in training to be successful (lame), and they see us as nerdy calorie counters who obsess over power numbers and lactate thresholds. We are both right. As a result, we should treat mountain bikers with respect, but expect to receive the same respect in return. We both recognize the other as an acceptable way to spend one's time, but think that our particular version is better.
Worth noting is that the guy who shows up on a group ride on a fixed gear. He isn't a hipster, he's a moron. While fixed gear bikes have their place (the velodrome), and some people (not me) might attest to their credibility as training tools, they are absolutely not for riding in groups with other people who have made the leap in technology to gears and brakes.
Triathletes are NOT road cyclists. They think that they are, and for this reason, they are potentially the most dangerous sect of cycling from both a stylistic and safety standpoint. The job of even the very best triathlete is to ride at a moderate pace for 4 hours by themselves. Most people you will encounter are "finishers" who just bought their first bike and don't find it odd that their brake levers are nowhere near their hands most of the time. Triathletes are responsible for sleeveless jerseys, those water bottle cages that mount behind your seat, and the idea that riding a bike in a thong is ever a good idea. None of it is a good idea. Plus running hurts. Not like cycling hurts, running hurts in a way that is stupid. Anyone who thinks running is a good idea is suspect in the first place.
Triathletes are horrible bike handlers because they don't train or race in groups. Even professional bike racers have a hard time controlling a bike at speed in those aerobars. (Menchov in the rain, Rasmussen like 4 times at Le Tour.) For this reason they are to be avoided and treated as dangerous. Let them pass if you're on a bike path, otherwise you'll be going faster than them. If they think it's okay to grab your wheel, slow down so they don't think you're acknowledging them as existing on the same plane that you do. They don't.
People on road bikes with skinny tires. That's us. This is who we'll be talking about for as long as I can come up with ideas for the blog, so summarizing here won't be useful. This is going to be fun though.