Of all the group rides that I have participated in, there is usually a set of characters who fit some sort of template.
The fearless leader: An excellent leader is a key to having an awesome group ride. One who knows the trails and the current conditions well, one who picks the right pace at the right time. Those leaders are not very memorable. The fearless leader (FL). FL can take a couple of forms, maybe he's the guy who goes mach chicken on the busy multi-use path, but most of the time he'll head straight for the trails that probably shouldn't be ridden on that given date by that group. The FL finds a sick enjoyment in the overgrowth, mud puddles, deep snow, anti-flow, and ultimately walking that his chosen trails usually involve. His dismounts and remounts are more fluid than even the most seasoned cyclo-cross racer. He must be fueled by the cursing from the other participants on his group ride.
The successful businessman: The successful businessman (SB) will be easy to pick out as he will show up to the group ride in some high end German SUV and then unload his wünderbike from the tailgate. However, once the group hits the trail or the climbs, SB shoots right out the back. After a lengthly wait at the next trail intersection, SB shows up gasping "I've been working too much", "I've been on business trips sleeping in hotels and eating in restaurants". While slow, the SB enjoys his freedom, not even a fearless leader can ruin his day. And hey, be greateful that he is spending his rare time off with you guys, his family is probably more neglected than his bike riding.
The shop rat: Most people ride their bikes to get away from the stresses of work, the shop rat seemingly never stops working. A group of mountain bikers is exactly his target demographic and he is not afraid to throw out some bikerumour.com advice to the other participants: "hey, you totally would have cleaned that climb if you were on a 29er", "yo, check out my 1x11 drivetrain, no more front derailleur, no dropped chains". Hilarity ensues when the product the shop rat has been plugging the entire group ride fails.
The wheelsuck: What is seen but never heard? The wheelsuck (WS). He doesn't talk much, but he is seemingly always locked on your wheel. Descents, climbs, he impossible to shake, and is just begging you to sink to his level and attack. You don't want to get dusted by a midpack novice rider do you? Take it as a sign of admiration. Accelerating out of corners and over hills is a great way tire out the WS, who after a couple furious efforts to close the gap, will eventually tire out like a dog.
The World Champion of Training: Similar to the WS, except the World Champion of Training (WC) has accepted that even though he is strong enough to stick with the top guns on the group ride, his race results show a different story, and he is willing to joke about it at his expense. As humiliating as it it is to have some midpack novice rider ride you off his wheel, you have to feel for the poor fellow who just can't put it all together on race day.
Mechanical: This guy's path has been crossed by one too many black cats. Pretty self explanatory.
The Panacouke: I think it's Dutch for "pancake" and I've heard of a certain Dutchman describe some riders as pancakes. I prefer to use the term for that guy who crashes on every descent, dabs on every climb, and instead of taking a fiver, he holds up the group and wobbles back onto the trail. He's probably semi concussed or at least winded, but being in the 4th position on the group ride is very important to him.
And then there's everyone else. People who are just out there to go for a rip!