In The BFG, Sophie is given clothes by the friendly giant.
One of the items is a red velvet jacket. After she picked it up, she flips it inside-out, and wears it with the red velvet inside.
I don't remember any explanations being given. Why does she do that?
What I took from the film is that she realized it had upset the BFG when he saw it. His response to seeing her wear it, "Where'd you get...", after he just dumped out a pile of clothes for her, was odd.
Since she was likely still in need of a coat, but didn't want to upset him, she turned it inside out.
A deeper answer which is the conclusion i came to, and i have found your posted question while searching for confirmation, could be to do with the BFG himself. When the other giant enters with a "booboo", during the scene he (i think either bloodbottler or fleshlumpeater - a discrepancy here between the 1989 animated and current version of the film) says something about a pet and a desire to eat it. Perhaps the BFG had a previous captive, why else would he have a basket of clothes. It also explains why he is so protective of Sophie as the logical conclusion for the whereabouts of the previous child would be dead. Seeing as the BFG has a large interaction with children and dreams it could be a logical summary.
She sees that it bothers BFG and when he puts her the first tree room all the dreams one she hears that's when she turns it inside out
