I have a guy in my group who seems hellbent that if he grabs an ally, he can teleport with them. Couldn't find anything in the PHB so I'm asking if anyone has any hard evidence against this. Really getting frustrating. Thanks.
You can only bring a grabbed ally along when you teleport if you have teleportation as a movement speed, not if you use a power to teleport.
From the Rules Compendium, p244 (emphasis mine):
Move a Grabbed Target
Action: Standard action
Strength Check: The creature makes a Strength check opposed by the Fortitude of the target it is grabbing. The check automatically succeeds if the target is a helpless ally of the creature.
Success: The creature can move up to half its speed and pull the target with it. The creature's movement doesn't provoke an opportunity attack from the grabbed target, but the movement otherwise provokes opportunity attacks as normal.
Moving a grabbed target is a standard action. Unless you have teleportation as a movement speed and therefore don't need to activate a power to teleport, you can't bring anyone with you; this is because you can't take two different actions simultaneously.