Is it OK for a dinner guest to help themselves to a host’s wine cellar?

Hello there! I'm Dr. Vinifera, but you can call me Vinny. Ask me your toughest wine questions, from the fine points of etiquette to the science of winemaking. And don't worry, I'm no wine snob—you can also ask me those "dumb questions" you're too embarrased to ask your wine geek friends! I hope you find my answers educational, empowering and even amusing. And don't forget to check out my most asked questions and my full archives for all my Q&A classics.
Dear Dr. Vinny,
Is it OK for a dinner guest to help themselves to a host’s wine cellar?
—Robert, Prairie Village, Kan.
Dear Robert,
Unless I’d expressly encouraged a guest to do so, I would be shocked and probably pretty angry if a guest helped themselves to a bottle of wine from my cellar or wine cooler. But I’d also have to ask myself if my hosting duties had somehow fallen short if someone was so thirsty as to raid my cellar ….
And I can think of a couple of exceptions to this rule: Certain family members would get a pass, and I have a friend who prefers cocktails and he knows he’s welcome to make himself whatever he likes from the bar—I even made sure to stock my bar with his preferred cocktail-making tools and ingredients. But ultimately the answer to your question is a very firm no: It’s not OK for a guest to help themselves to a host’s wine (or anything else) unless it’s been expressly put out for that purpose.
There’s also a lot of confusion about bringing wine to a party and whether or not a host should open the bottle, so check out my archives if you're in search of more etiquette advice on bringing wine to a dinner party.
—Dr. Vinny