Q:

In multiplayer, can a player concede abusively?

Arnold, Beth, and Chuck are playing a multiplayer game (e.g. Commander or Free-for-All).
Arnold has Maralen of the Mornsong:

Players can't draw cards. At the beginning of each player's draw step, that player loses 3 life, searches his or her library for a card, puts it into his or her hand, then shuffles his or her library.

Beth has Dictate of Kruphix:

At the beginning of each player's draw step, that player draws an additional card.

Currently, it's Chuck's turn. He begins his draw step, and chooses that Dictate of Kruphix's ability go on the stack, and Maralen's ability go on top of that. Because Maralen is on the board, Dictate's ability is essentially useless (Maralen prevents players from drawing cards).
Using Maralen's ability, Chuck tutors up a card. Suppose Arnold really hates Beth. After Maralen's ability resolves, Arnold concedes. Because Arnold has conceded, Maralen is no longer on the field. 

800.4a When a player leaves the game, all objects (see rule 109) owned by that player leave the game and any effects which give that player
  control of any objects or players end. Then, if that player controlled
  any objects on the stack not represented by cards, those objects cease
  to exist. Then, if there are any objects still controlled by that
  player, those objects are exiled. This is not a state-based action. It
  happens as soon as the player leaves the game. If the player who left
  the game had priority at the time he or she left, priority passes to
  the next player in turn order who’s still in the game.

Chuck now proceeds to draw 2 cards (1 from the draw phase and 1 from Dictate of Kruphix).
Obviously, this isn't an ethical thing for Arnold to do. But is it within the rules of the game? Or am I mistaken? Would something else happen instead?
A separate question: would this result in Arnold being banned from future tournaments?

A:

The rules say you can concede whenever you want to:

104.3a A player can concede the game at any time. A player who concedes leaves the game immediately. He or she loses the game.

This is kind of unavoidable, because people have to be able to pick up their cards and leave. And it's certainly possible to use this spitefully, whether via your scenario or another. (It doesn't even have to be something fancy - just dropping out a turn before your inevitable death can swing things.)
Many people adopt house rules in order to curtail that sort of behavior. It's hard to define clearly what is and isn't acceptable, especially since you can be plenty spiteful even without ever conceding, but if you play with people you get along well enough with, you may be able to get away with "don't be a jerk". More broadly, if you do things that make you miserable to play with, you might quickly find yourself not having anyone to play with.
As for tournaments, well, there aren't really serious multiplayer tournaments, and so the Magic Tournament Rules don't have anything explicit about multiplayer. There is potentially commander at Friday Night Magic, and if they're abiding by the rules, they'll have to allow you to concede at any time. But while I don't think the store could actually kick someone out for making a spiteful concession, the same about being pleasant to play with probably applies there: it's a local store, with many of the same people coming repeatedly.

A:

This is NOT a rules based answer. 
I have not played Magic for some time, but when I did play there was a simple house rule (for multiplayer). 
If you conceded, you could not play the next "game" either. The general idea is that concessions were not supposed to be tactical things in multiplayer, but to fill the need of "I gotta go"
Kind of the same way with being dealt out in poker.  If you miss the blinds then you have to wait for them to come back around. 
That said, there was no rule that said you could not concede. So some people did, just to get their friends a boost. Those people usually had a hard time finding others to play with though.

