For those of you that have played World of Warcraft in any group (which, reading this blog, you probably have) know a little term called "aggro". Each mob (or enemy) has what is called as an aggro table. Whoever is at the top of that aggro table is the person that mob will attack, generally speaking. So, to look at the 3 roles: Tanks want aggro while Healers and DPS generally want to minimize their aggro so that they don't exceed that of the tank. (In some cases, DPS is the tank, but that's not the focus of this discussion.)
Different classes have various ways to deal with aggro, hate, or threat, as it is sometimes called. Tanks (warriors, druids, and paladins) have abilities to increase aggro. They either do this by directly damaging the mob or using a skill that is intentionally designed to make the mob focus on them, called a taunt. I assume you understand this concept, and if you don't, do yourself a favor and take a look at the spells that those classes perform. There's more than a few of them that say something to the effect of "causes a high amount of threat." As a tank, you'll probably want to use these skills a lot.
Some of non-tanks have ways to shed aggro. For example, every 30 seconds, a hunter can feign death, and as long as it's not resisted, the threat towards him is completely erased. Every 5 minutes, a rogue can instantly vanish and erase his aggro. Paladins can help all of the people in this role by casting Blessing of Salvation. And for my final class example, a mage can cast Invisibility every 5 minutes, but it takes 5 seconds to have the full effect in which time you can't cast anything or be hit or you'll have wasted it.
All that should be review for you. If you need more details see Threat or Aggro over on WoWWiki. Today however, I'd like to focus more on two other types of aggro that are just as real and maybe even more dangerous, but I haven't been able to find them listed on WoWWiki yet.
Parent Aggro. Generally caused on school nights when you're up too late. A large amount of threat can also be generated by failure to do chores, homework, or upon obtaining bad grades because of outside factors (especially playing Wow instead of putting forth the needed effort). This is a very specific type of aggro. Generally speaking, you can only get on an aggro table of two "mobs" in the world by generating this threat. Normally it is easier to aggro the female mob vs. the male mob. But once equally aggroed, they're both a force to be reckoned with. This type of aggro can cause you to lose a precious healer at 1 am (healer's local time) on a Thursday when you're about to pull Nightbane.
Spouse Aggro. This is probably more well known as Wife Aggro or generally mispelled as Wife Agro. To keep this post non-sexist, we'll use the gender neutral term. This is the more severe of the two "unusual" aggros. Your parents will always love you even if you "waste you life away playing stupid video games," but your spouse may not. Causing Spouse Aggro can cause long periods of afk, but usually for days at a time. Normally upon pulling Spouse Aggro, one must work hard to repair their reputation with the mob. Gifts can work well, but generally just spending time with the "mob" will raise you from a KoS reputation level. Akin to Spouse Aggro is also the GF/BF Aggro, and to a much lesser extent, the Children Aggro. GF/BF Aggro may need to be assessed, because it may eventually develop into Spouse Aggro, but excessive aggro at that stage may cause one to reflect if said aggro is really necessary at all. Children Aggro varies, but can usually be reduced by bed time, nap time, movies, candy, or other mind detouring activities.
Be more wary of pulling these types of aggro far more than anything else in the entire game. They are dangerous. They need to be avoided at all costs. Work hard on the reputation with said factions, and you shouldn't have an issue.
Are there other types of aggro that I missed?