Have you ever wondered what it would be like to meet a famous person? Or for those of you who already have met a famous person, were you just so starstruck that all you could manage was a selfie and a lame hi?

A few years ago, my grandmother's friend, Carol, was preparing to meet Chief Justice John Roberts (as in the head of the Supreme Court) at a friend's party. Knowing of my interest in the law, she offered to get his autograph for me. Since the party was in Massachusetts and hosted by people I didn't know, I couldn't snag an invitation or afford the plane ticket to go.

But what if I could have gone to the party? What would I have said to Chief Justice Roberts? What would I have done? Here are some things you should and shouldn't do if you ever meet someone famous, according to the celebrities themselves.

1) Don't tell them they look tired

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According to Ryan Seacrest, even if celebrities do look tired they don't want to hear it. It will only make them angry.

2) Don't point out they look like another celebrity 

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While some celebrities think the cases of mistaken identity are funny, other celebrities like Daniel Radcliffe (who often gets mistaken for Lord of the Rings star Elijah Wood) and Daisy Ridley (who played Rey in Star Wars and gets mistaken for Keira Knightley) get pretty upset with fans whenever they make the comparison.

3) Shower them with compliments 

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According to Ryan Seacrest, when in doubt compliment them. It always works

4) Don't touch them

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This is a big one and not a rule people always follow. Ryan Reynolds was very uncomfortable when a fan high fived him. At the time, the fan was helping his sick wife onto a stretcher and Ryan Reynolds felt it was inappropriate to get high fived in such a serious, high duress moment.

5) If they are spending time with family, don't interrupt them

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Claire Foy, the star of The Crown, was talking to her mother when a fan interrupted them for an impromptu meet and greet. While Claire humored the fan, she was also a bit annoyed at the pushy fan for interrupting her mother-daughter time.

6) Let the celebrity know how much they have impacted you

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Celebrities love it when they can make a difference in someone's life. Meghan Markle, a former actress turned princess, was so happy to meet and greet a fan whose life was changed after Meghan helped encourage the young fan to be herself.

While it's cool to meet a celebrity, don't tarnish it by being a butthead.