In all groups of people there are certain dynamics that take place. Depending on what type of group certain types of people will always exist within them. While each group will vary somewhat, but so long as there are three or more people certain dynamics are in play.
In a group of men there will at the very least be three people in play. There will be the dumb guy, he may not be generally dumb, he is just not at quick as the others. The dumb one is slow with comebacks, and might not be the best at arguing a point. Next we have the wimpy dude, he avoid confrontation at all costs, and has no opinions of his own. The wimp is in the group mainly because he needs somewhere to get his opinions from, and to have people to help him move heavy things he is to weak to move himself. The third man is the lazy man, never awake before noon, never to be relied on for anything. The lazy man is usually an expert on some area of useless information, and makes others feel better for being more motivated. These three are the most basic members of a male group. Larger groups will add more, like the driver, the fat guy, and the guy that everyone wonders why they are friends with.
Female groups also have their stock characters. In a group of women you will find: an "ugly" one, a "pretty" one, and a "bitchy" one. All of these terms are in quotes because they are very relative terms. The "ugly" girl is just less attractive than the others, in a group of 10s she might be an 8, while and 8 is still attractive it is not as good as 10. Same applies to the "pretty" one, every one else is a 7, she is an 8, you get the point. Now the "bitch" is just the one that is generally hostile to those not in the group, she might be nice to others in the group, but if you are an outsider, or a man she simple doesn't like, watch out. Larger groups will also have: eating disorder girl (either to fat or to thin), tomboy, crazy chick, and everyone's favorite the easy chick.
Keep in mind one person might fill two roles within the group. You might have the a guy that is both the dumb guy, and the wimpy guy. No terms are necessarily a put down, sometimes the dumb guy is the leader of a group. Remember, you think your group doesn't have a certain member, it is likely you are that member.