I'm not getting the whole 'your player is being abusive' and 'you are letting them walk all over you' responses.
It seems like you and your group are having a good time.
It seems like you give them liscence to push the rules to limit and think outside the box.
But you find that your Bard does it in a way that sometimes gets on your nerves? Or just tries to push you so often that you are getting a little annoyed and need to express that and get some feedback from fellow players?
In the specific case of the teleport from the worm:
It seems from reading the thread that the interpretation of the legality of the PC from inside the worm is far from clearcut.
The worm does have a special mention about the fact that swallowing cuts off LoS/E. That's a fairly good indication for me that you're right to think that it would cut them off from the Bards magical effect as well.
But the fact is that the Bard's ally is about to die in there? Is that right? 2hp left and probably suffering from gastric acid burns? (I am not familiar with the creature) This is when I would hope that my players would try and pull something out of their Rs and save their friend.
This is why I have added a houserule to my game (stolen from PCat's game). Each player has an encounter power called 'Do something Cool'. They can use it to alter their powers or magic items' effects in ways that make sense or interact with the 'terrain' in awesome ways etc. etc.
When I had a situation like the one you describe, which comes into the grey area of 'I'm not sure you can actually do that', then this solves that problem no fuss. Of course the player would have to tell me how that works: 'I wait until the worm opens its gaping maw to roar, and just at that moment I fire 'enter power's name here' down its throat sending arcane waves of fey energy down into its belly and teleporting Frank from inside, away to safety.'
The cool thing about adding a feature like this to the game is that players start thinking: 'what do I want to do' as opposed to 'what can I do', which is an awesome element to have in the game. It certainly keeps things dynamic and the DM on their toes.
It also means that ALL the players have the same chance to bend the rules in exciting ways once in a fight.
It also means that players who want to bend things a little too far can't do it every single time, but often enough to keep them well happy.
As for the Beetles: Not awarding XP not only 'punishes' the Bard, which you say you wanted to do to teach him a lesson that he shouldn't act without consulting the group, it also effectively punishes the rest of the group as well, for something they had no part in. Do you really want to punish a player for having a good idea? Do you really need to teach the player anything? Is that even your role (he seems to know the game well enough). Surely acting alone without consulting the group would quite naturally inform the player of the consequences of doing that when eventually it happened in a siuation where it simply backfired: Imagine he rolled a natural 1 on his imitaion (bluff) check: 'Oh, dear, it seems you have accidently imitated the beetles mating call ... and they all seem suddenly very excited, scuttling directly towards the source of the call... that is of course... towards you'. If you didn't want to reward him for going rambo on the group, maybe you could have given the group xp equal to a minor quest and told him: 'normally I'd give you full XP. It was a good idea and it worked, but I don't want to encourage you to make decisions on your own that affect the entire group'.
Or as others suggested, you could have turned that into a simple skill challenge: 3 successes needed: Nature to know about the beetles natural enemies, and to know what sound that creature makes, Bluff to imitate that noise and maybe arcana to stir the wind? (dragon swooping) or cause a shadow to flit across the rock? And there you have the XP sorted out that you can fairly award the group. It would alo give the other players time to get in on the act and help out with the ruse, and get to feel part of the Bards actions.
Double Crit: That's a house rule you've brought into the game. Anyone could have rolled it. You can't resent a player for having hot dice. And I guess you have to deal with the consequences of introducing a house rule that can kill a creature outright. You could alter it and make it deal 'bloodied damage' to the creature, or hold the right to reduce a double crit on a major villain to 'bloodied instead of dead'
[MENTION=11586]RigaMortus2[/MENTION]: The Rule of Thumb is rubbish advice, and I think you probably think that yourself too. Besides, what do you mean by referring the OP to the Rule of Thumb? He's totally open to everyone's rule's interpretations/clarifications, and not arguing with anyone at all.