IMHO, there was absolutely nothing gratuitous about Jack washing his clothes in the buff. I mean, when you are on top of a mountain and that removed from all signs of civilization, at one with nature, I would DEF have done the same thing. I would imagine that given the circumstances he/they were in, one would lose their inhibitions very quickly. One would feel right at home being naked...
I think you're quite right. Perfectly normal behavior, especially when there aren't too many clothes (as the book says).
But this scene is just one of many (a real and specific theme by Ang Lee I think) expressing the natural flow towards an increasingly
mutual and
domestical camp life (I shd say camping life).
Within all the general camping activity like packing horses, whittling in the tent on a rainy day, etc, there are several overt scenes which I think are meant to show a deepening common life. They cook a lot, with the camera pointed at the pan, less at Ennis. There's the Ennis washing scene, they put up a tent, they take it down, they drink often and in detail, from the same bottle; Jack's in the buff washing Ennis' shirt, etc. Jack goes off to piss (book makes a bit of a deal of this).
I think the creators are using these scenes to make the progress to an intimate life seem more likely, inevitable Proulx says.
The funny thing is, all the domesticity seems to take the place of overt romantic flirtatious behavior. I know a guy who was completely disappointed with the movie because all these opportunities for hard core flirting in camp
were wasted ! -- all this domestic stuff and almost never a
look, he said!
Yes I know about Jack's quizzical look at the campfire that makes Ennis say "What?" But that's
real slim pickins, if you want a "regular" romance like my disappointed pal.
What would a crude movie-maker have done with two fit young guys, deep in the woods, heading for the romance of their lives? Result would have been completely regular and banal, and banale. Unremarkable. We wouldn't be here now.
Obviously I prefer Ang Lee's subtle approach, as being 100 x more powerful. ("...a billion times ... lovelier, more dangerous...", as the poet Hopkins says.)
IMHO: in 1963 two straight macho guys would behave exactly as they did. With behaviors learned from a rural society that was much older -- think 1940s or further back. Jack's dad was probably born in the teens or 20s!
Domesticity helped overcome the numerous barriers to their deeper involvement.