It can't be against the rules because the rules only apply to "affecting the gameplay of other players" but this guy isn't engaged in any form of "gameplay". And he's already breaking the rule by affecting everyone else's gameplay.
Not that it matters much since I believe almost all that complaint type of stuff is automated.
get technical all you want it falls under harassment. you are going out of your way to do something to him. unfortunately his game play at the time is sitting still. We can nit pick it all day but i can tell you getting a group to self destruct on him would more than likely be considered harassment, which is clearly stated as against the rules.
The afk problem sucks but Cryptic is the group that created it. Not the players, I do not nor would I EVER condone AFK'ing for entire matches, that to me is just bad sportsman ship.
I wish you luck in dealing with it, I do, but all things considered, this is a side effect of grind play style. Why work when others can do it for you.
The problem with team-killing them, or letting the other team do it is that it doesn't PUNISH the AFKer at all. They still get their dilithium, and the Arena was still ruined for everyone else. The only thing that will help is a system that doesn't let the AFKer get his dilithium. That's the ONLY way they will ever stop doing it.
If Cryptic gave a crap about PvP, they'd fix this.