He talks about them as if they're a brave platoon of soldiers on a vital mission, suffering intolerable hardships
Love this! 
The thing is... offering to do two straws is a very normal thing to do and would be what I would've done. OK Martin kept on a bit, but they know his character and to keep mentioning it like a child would, did not deserve being put down in such a nasty way like Larry did.
I imagine Larry is literally just doing this for the money. He isn't in it for the experience. He's just coasting along, he's managed to be exempted from quite a few tasks and now as the days/weeks go by some of his camp mates are getting on his tits and he can't help but have a pop at an easy target like Martin.
I honestly think there's nothing wrong with Martin, to give him his due, he's thrown himself into every single task, he hasn't whinged. Larry just hangs around with a miserable face, at least Martin is irritatingly cheery!