If you've ever been ganked by a twink in 10-19 WSG, you might chuckle at poor Neflm's predicament. He accidentally leveled his Witching Stave-wielding Warlock twink to 20. Apparently all it takes to kick a twink out of the battlegrounds... is 200 experience.
Of course, this is exactly what that XP toggle is for, if Blizzard ever chooses to implement it. Or if you want to go the other direction, you could just award experience in the BGs, which would definitely put a stop to twinking forever (and make Neflm's problem much more common).
But he can't be too distraught-- even if he's accidentally leveled his 19 twink to 20, there's always the chance to be a terror at 20-29. As even he says, in the comments, "at least Stonetalon should be a cakewalk."