I've had this photo for some years and just love it. How many times can you say you've seen a WW2 German soldier wearing a Pickelhaube? Willing to bet he was a veteran of the Great War.
A really cool photo
But the way he's about to laugh, it's certainly a spontaneous private photo. The fact that the helmet has neither cockades nor chin straps also suggests that the men found the helmet somewhere and thought it was funny how they looked with the old helmet.
However, he will not have worn the helmet on duty. But still a funny pic
My first thought is the alcohol is involved and that it might be a GI during post war occupation duty. It would be the only time GI Joe dressed up in enemy uniforms and headgear. Just a SWAG on my part.
Best regards
John