heart of the mountain;

Well, to me, an accidental bagginshield proposal would occur one of two ways:

1) let's say that in dwarven culture (headcanon), giving your intended a great gift like a family heirloom or something personalized, would be a form of proposal.

Thorin giving Bilbo the mithril mail could have been his proposal, and while the other dwarves and Gandalf understand the meaning, Bilbo doesn't and no one tells him bc to everyone it just seems obvious. Everyone starts treating him with the same regard that they do with Thorin, their leader, and Bilbo notices the change in demeanor and asks either Bofur, Balin, or even Gandalf about it and they're like "Mr. Baggins, didn't you know? Thorin proposed to you, you are his consort! Congrats on being the only one to get through his rock solid heart!" And then he says something like, "I'm sorry, what?! What do you mean I'm his consort?!" "Don't you remember, when Thorin gave you the mithril vest? In our culture, giving a fine gift like that to your intended is a proposal! And you accepted his gift, so you sealed the deal." And Bilbo tries to tell them that he didn't know, that this is a mistake. But when he's asked whether he would like to return the gift and end the proposal, he can't do it, he doesn't want to, so he just goes on with the knowledge that he's the King's consort. Thorin would be so pleased that now he can be touchy feely with Bilbo, and it wouldn't really be much of a change from what they were like before, but now everyone knows and accepts. (And if you want the angst feelings, the scene at the end where he tells Balin what he feels about Thorin after he dies hits harder.)

2) if Bilbo proposes: like I said, I need a refresher on the lore so if there's a canon explanation for a Hobbit form of proposal or anything, just excuse me and let's pretend.

So, hobbits really love food and simple living and comforts, right? But that's not really possible when they're on a long journey, so Bilbo has to make do with what he has. Maybe they're short on their food supplies one day, and Bilbo has some food from back home that he packed and it's wrapped in a nice package, and he was saving it for himself, but offers it to Thorin and Co. And we all know Hobbits love to eat, and they eat a lot, so a few rolls of bread is like a snack to them, whereas for others it's a full meal, so the dwarves think he has a feast and is enough to feed them all for the night. Bilbo unintentionally proposed to Thorin by giving him a gift of a homemade 'meal' in a nice package, as is the custom (headcanon), and for a moment Bilbo forgets about it and just feels good for providing his friends with some food. Later that night, Gandalf reminds him, teasing him, about his proposal and Bilbo blushes and coughs nervously, saying he didn't mean to, but luckily, neither Thorin nor the other dwarves know about it so he thinks he's safe. But, Kili and Fili, sneaky little guys, were eavesdropping on their 'private' conversation and rush to let Thorin and everyone know about the meaning of Bilbo's gesture. Thorin scolds them for being nosy and that they probably heard wrong anyway, but the next day Thorin asks Gandalf and he confirms. Thorin says nothing but now that he knows, he allows himself to get physically and emotionally closer to Bilbo and from there, they kinda just live as a couple and no one questions it, they're happy for them!

It's been so long, but this is bringing back my bagginshield feels from back in the day 🥰