I've never met a celebrity in the wild. All the times I've met celebrities were at specific signing or meet and greet events, but I know a day will come when I'm standing in the security line at the airport, or grabbing a bite to eat when I'll spot a familiar face.
I'm often too shy to speak (even when I have time to prepare what I want to say) to people I look up to or find influential. So, I don't imagine myself being the type of person who would approach them directly for a picture or autograph, even if in a completely appropriate context.
Despite my own hesitance to approach a celebrity and ask for a photo, it is certainly an occurrence they have become accustomed to. In most instances, celebrities seem genuinely delighted to be asked and take a few seconds to allow you to snap a selfie. However, there are always those stories someone you know has or that come out where a celebrity was "rude" for denying a fan a photo (especially if they had granted someone else a photo).
However, as people who can pass through life with near anonymity, I think it is important to acknowledge that celebrities are people, too.
They are allowed to be exhausted, grumpy, have bad days, and want nothing more than to eat pizza and watch Netflix.
They are allowed to have insecurities and deny a picture because they don't feel confident that day. Thinking or believing otherwise is painting an unhealthy picture of celebrity and fame in our minds.
Celebrities are not robots programmed to take selfies with you 24/7. Imagine not being able to walk outside your house without your photo being taken or not being able to eat dinner without someone approaching and asking for an autograph. For many non-famous people, this would be overwhelming and frustrating. And even for famous people, it can be overwhelming and frustrating.
I'm not saying don't approach or ask celebrities for pictures, as long as you are polite (regardless of their answer), I feel this is a harmless interaction. On the contrary, in some cases, it is rude to ask. If you see a celebrity with they're family or in an obvious important moment, I think it's important not to interrupt. It is not often they can just be a person and enjoy time with family. Even if others are asking, allowing them to get back to whatever they were doing is something they will silently thank you for.
Long story short: respect celebrity's autonomy.
Next time you see a famous person in line at Starbucks or somehow stumble across a film set, think twice before asking your favorite celeb for a selfie. Is it an appropriate time? Do they seem to be in a good mood? Is it obvious they don't want to be noticed? Even in the "pics or it didn't happen" era, it's important to recognize that the most important part of meeting a celebrity is just that: the meeting.
It's the conversations and experience you share with them that matters rather than the Instagram likes.