I will often have a question at the tip of my tongue to ask someone, but then I realize it probably sounds snarky so I don't ask, but often these are genuine questions that I want to know the answer to!! You'll see what I mean (try to reduce the level of snark when you read them to yourself):
Why are you buying a case of bottled water? Are you travelling to a place where the water is not clean? I can think of no other reason.
Why do you buy your breakfast/lunch everyday? Don't you know how much money you could save by bringing your food from home? And how much healthier it is?
How are you wearing jeans in 30+ degree weather? Do you not feel the heat? Are you not comfortable in any other item of clothing?
(And conversely) how are you not wearing a hat or scarf when the temperature is so cold? Do you not feel the cold? Are you just worried about messing up your hair?
Why are you ordering so much from Amazon? Do you really need all of those things?
Why don't you wear a helmet skiing or biking? I know you may have complete confidence in your ability as a skier/biker, but it's more just about the people who could run into you. Natasha Richardson (Liam Neeson's wife) sustained a head injury and died by falling backward while skiing and she was just standing still at the bunny hill.
Why do people (mostly women) crouch down when taking a group photo? Most of the time they aren't really blocking anyone behind them, I always think it looks so awkward.