Often used, more often misused, the AFK is a safe and viable choice when deciding how to escape imminent PvP. More than that, however, it is a tool that lets other players know that you won't be able to appreciate their awesomeness, at least for a while.
Here is a quick guide to the plethora of AFKs and their meanings:
"AFK/afk" - The plain cake donut of AFKs. Often typed in haste and accompanied by a typo, this AFK lets people know that you have to step away from the computer, and you have no time to explain. Based on your capitalization, the first and simplest example can take on different meanings: if you type with no capitalization or punctuation then when you type afk it will not be any great difference but if you type AFK then you are clearly excited about something either good or bad; conversely, if you usually type with flawless capitalization and punctuation, then a simple "afk" may be a warning that something is wrong or that you're frustrated with the way things are going.
"AFK one sec" - Approx. 5-60 seconds - The first of the conditional AFKs, in terms of length. By expressing a timeframe for your departure that uses a short time measurement (sec) and detailing a exaggerated estimation of how long it will take, you're taking great care to assure other players that your AFK will be very brief. Best used by the honest rather than the stupid, since if you're gone for too long after this one then people tend to get annoyed. Still, there is no excuse not to wait for somebody who is only "AFK one sec".
"AFK a sec" - Approx. 30-90 seconds - Similar to "AFK one sec" except in length; this AFK will tend to be slightly longer in duration while still taking the time to assure other players of your impending return. This AFK and the one above usually refer to distances from the computer not exceeding the room the computer is in. If there are turn/level spells such as Ghostly Visage in place, your allies are better off continuing the quest, provided that your character is not pivotal to the group strategy.
"AFK a min" - Approx. 2-5 minutes - An AFK of rare usage but with a very clear and defined importance: the duration of an "AFK a min" coincides well with a bathroom break or the microwave preparation of food. Allies should consider whether or not to take a brief break from battle, advancement, and exploration during this time; if time is of the essence, due to buffs wearing off soon, then it is probably best to leave the other player.
"AFK a bit" - Approx. 5-60 minutes - Not an easy AFK to predict in regards to duration, "AFK a bit" often means that you don't know how long you'll be away exactly. Some people like to use this one for extended absences, during which many people will pass by and marvel at the great unmoving character paying homage to Grumbar. When you use this AFK, you've forfeited any participation in immediate events and would be better off finding a safe place to hide or logging off. Allies should not count on you to return any time soon, just to be on the safe side.
"AFK: Fire" - Approx. ??? - Your shit is on fire. Damn.
"AFK: Tornado" - Approx. 1-4 minutes - Rare and unique, the Mewtwo of AFK if you will. This is an AFK that must not be ignored, considering the gravity of the IRL situation. In addition, your patience will be rewarded with information on tornados when the player returns. Here's a couple of examples: https://efupw.com/efu1-forum/topic/32/32979/afk-tornado/index.html#post-130492