Never been in that situation so it's hard to say for sure. It is easy to guess at what you would, but it actually happens things usually turn out different. I don't know, if it a camp type thing maybe talk to the kids dad and the others in camp to get thier opinion and maybe sit down and educate him. Not berate him, just let him know how you guys think those situaitions should be handled.
If he was cockey about it I probably would have been a little ticked and there would have been a situation later for sure. There is no reason for a 14 year old to get lippy with an adult in my opinion. If I liked the kid though I might have played it off like he killed it and let him have the moment, especially if it was his first deer.
At this point you probably just let it go though. (did I really just give that advice?)

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I hope everything works out for you in the future.
Paul