AFK feature wins. I leave for 5 seconds and people have whispered a ">.<" to me because I didn't answer them. It should somehow be tied into whisper mode as well, it needs to tell whoever is whispering you that you are gone, not just people that are in your sight.
Just posing AFK or BRB or BBL in chat doesn't work for many reasons.
1. More posts = it's gone up in chat, where no one will see it
2. People in other maps won't be able to hear it, and you don't have time to whisper everyone you know, saying "AFK"
3. Whoever you said "AFK" to, could've gotten back from an unsaid AFK themselves, therefor, not see it.