Between the show and various side projects, I feel like there's probably enough moments supporting a headcanon that Ruby tends to just. take Weiss's stuff. and not necessarily asking first
and i actually think this is a general thing with Ruby. if she likes you, she will be taking your stuff without asking. the more she likes you the more stuff she'll take. Yang explains this to Blake at some point after Ruby takes something of Blake's, and right as Yang says that second bit Ruby walks by with a comically absurd amount of Weiss's things
Weiss, understandably, would not be happy about this at first. I feel like, at some point maybe between Volumes 2 and 3, they'd have a conversation about boundaries and stuff and where the line is between "things of Weiss's that Ruby can just take without asking" and "things of Weiss's that Ruby really should ask about first"... and even though Weiss is the one drawing that line and if she told Ruby to stop taking her stuff at all Ruby would definitely respect that, the line ends up being almost exactly where it would have been if Ruby had drawn it
Before that conversation happens though, I can imagine - during late Volume 1/most of Volume 2 -
An escalatingly absurd series of attempts by Weiss to stop Ruby from taking her stuff (she has not yet had the idea to just talk to Ruby about it)
Weiss trying to get revenge by taking Ruby's stuff and seeing how she likes it, which backfires because not only does Ruby not have a problem with it at all, she saw Weiss wearing her cape and told Weiss she looks cute and now Weiss's face is the exact same shade of red as that cape
