[Rumil]

I think Gandalf is being a bit tetchy, not without some justification!

Here they are deciding the fate of the free world and Pippin is making light-hearted, if not downright silly, jokes.

But remember that Gandalf argued in favour of allowing Merry and Pippin to go on the quest, against Elrond's advice. Maybe he's having some second thoughts at this moment!

Saying the name of a 'Wizard' out loud was traditionally considered a bad move in some cultures, as it somehow focussed their attention on you, even at a considerable distance. I can't offhand think of anywhere where this is clearly stated in LoTR but might have been at the back of the Prof's mind when he was writing this?