To say that stuff = junk is really reaching, and splitting hairs unnecessarily.
Oceanus, do you mind if I move your stuff off the chair so she can sit down.? (I dont consider my purse and jacket to be junk, and I dont think anyone else did.)
Sometimes when a person is not well-liked, things they say are magnified and taken to be rude and offensive, whereas if someone else said the exact same words it would be okay. The subject of the initial post may very well be a busybody; I still see nothing wrong with what was said on either side.
In the example you gave, yes, I would agree that virtually no one (who was not totally paranoid) would equate the word 'stuff' as meaning 'junk'.
But if someone waved their hand around your living room and told you that you really should get rid of a lot of this stuff, then I think many people would interpret that use of the word as being equivalent to calling it junk. And in that circumstance, that interpretation would probably be correct and reflect the real meaning of the person saying it.
Junk means something useless and/or unattractive. Something not desirable to have. The way some people use the word stuff means exactly that. For a lot of people the words are virtually interchangeable except 'stuff' sounds a little nicer than 'junk'. The meaning, if it is used in that way, is the same.
After rethinking (yeah, we're allowed.........
Yes, a lot would depend on tone and mannerisms. I'm a neatfreak, but regardless, if someone made a certain movement with hands and said "You really should get rid of some of this stuff" in (what I preceived as) a condescending tone I wouldn't appreciate it. I might say, "Oh? I like it the way it is; don't worry about it". Then beandip.