Say you get to meet any celebrity you want - not necessarily in the arts/cinema like Downey or Clooney, but anyone. Such as Obama, etc.
How would you hold a conversation with them without them thinking, “Here we go again, the 500th time someone has said this?”
It depends, if it is just a meet and greet, assume whatever you say is probably something they’ve heard a 100+ times. I’m sure my questions and gushing to Yogi Berra were repetitive, but he was such a nice person that he made it feel like my questions and gushing were new to him.
If it is after a festival that you helped to put on and one of the band members comes over to hang out with the crew, just treat them normal. Offer them a beer, etc.
So situational would be my answer.
I’ve met and interviewed many well known people in music and all I do is take a second to put myself “in the moment” and imagine what I would day to any stranger sharing my bus seat. Improv classes have made this easier as well.
I’ve had a few occasions where I’ve had extended conversations with celebrities (a couple of actors, a couple of authors). Once I got past the “I really enjoy your work” stage, and tried to not gush too much, I found that it wound up evolving into discussing a particular thing that the person had worked on that I had mentioned, and that the actor or writer seemed to be particularly proud of / happy with.
For example, I talked with actor Ioan Gruffudd at a convention for maybe 15 minutes – he was doing a “guest of honor” appearance, but there was no one else there to talk with him. I mentioned that I had first seen him in the Horatio Hornblower TV films, and as his eyes had lit up when I mentioned it, we talked about his experiences making those.
Ask them how their day is going, and let them choose what they feel like talking about.
I met an author at an SF convention. I went up to him to say “Thank you, I’ve really enjoyed your work over the years, it’s brought me a lot of pleasure, and I look forward to your next book.” and I intended to leave it there. He said that actually having someone come up and say “thank you” like that was pretty rare. We wound up chatting for around a half an hour. So, presumably, that was not a “here we go again” moment for him.
How about trying to find a topic they want to talk about? Conversation 1 
A good one is “have you read any good books lately?” For example, Bill Gates was asked that question at an event I was at maybe 15 years ago. He really went into Guns, Germs and Steel (which had been recently published and I didn’t know existed), and then opened up and talked dad stuff about his kids. It was great, it felt personal, new ground, and 500 of my friends in the audience found it fascinating.
I’m pretty sure you could have a nice conversation and maybe get into other stuff with Prince Harry if you started out on his son Archie, then express interest or knowlegable questions on the Wounded Warriors/Invictus Games.
Author Michael Lewis was interviewed for The Big Short in Seattle at an auditorium with maybe a 1,000 seat capacity. The guy that interviewed Michael, was the Outward Bound counselor when Michael was an Outward Bound participant at 20 years old in the Three Sisters Wilderness area in Oregon. It was great. Not sure if the audience appreciated the 20 minute digression into Outward Bound, some old photos, one of the other participants flew in from Texas to sit in the front row. Fascinating to hear what the counselor actually counselled Michael on before he went to Lehman Brothers and really started his career with Liar’s Poker.
Of if you had run into Lenard Nimoy and kicked things off with “Really like your black and white photos” and then take it from there.
As Broomstick wrote above, it might be good to acknowledge you are a fan up front to get that elephant out of the room. Something along the lines of William Gibson, loved your books and neuromancer is my favorite. Any authors you might recommend I check out?
Be sensitive if said celebrity seems to want to be in their own space and not be chatted up by strangers. Toss out your opener, and if it doesn’t land, be politely on your way.
When I met John Marzluff at an Audubon thingy, I told him about how some Dopers (I did not actually say “Dopers”) had been saying that he was like a rockstar who rode around in a limo. He thought that was quite funny and signed my copy of Subirdia with “from the rockstar”.
I had a nice long conversation with Poul Anderson about the Mitra Cult.
When I was a City Commissioner I went up to then Mayor Clint Eastwood and told him he had a nice little town here. He bought us drinks. But he just thanked me, he wasnt talkative.
I had a long talk with Raquel Welch about Whales and Dolphins.
When I was working concerts, this was exactly my policy. Celebs will let you know, one way or another, their level of interest in dealing with you. My experience was some people can’t wait to talk to you. Others want absolutely nothing to do with you. The vast majority were perfectly fine with light chat or inane small talk. I generally would just leave people alone.
I went to some sort of random street festival because Peter S Beagle was there and I brought a few books of his to have them signed. Apparently nobody knew who the hell he was and he looked a bit bored and lonely so I sat for a while and we chatted and he was quite interested to discover that a poem from The Last Unicorn fits perfectly to the tune of “The Ash Grove” and that it was regularly performed at SCA events. He wasn’t all that familiar with the tune so he asked me to sing it for him and I did. He seemed quite pleased. A very kind and cultured gentleman, that one.
I don’t think celebrity entertainers, for example, ever get bored with well-behaved people paying them compliments, even ones that they’ve heard five million times before. One of the reasons people become entertainers is because they really want to connect with an audience and get that positive feedback and validation from them.
At a book signing, I got to be part of the “herd the customers past the author” thing and when Bill Bryson looked up from signing my copy of his latest book I told him that I couldn’t think of anything witty to say to a writer like him so I’d be happy to hear about his favorite pasta.
Despite him possibly making the unobtrusive sign for security to be ready, he laughed and (if I recall correctly) said he really didn’t have one. We exchanged a few more words and I got a couple more seconds than the people in front of me. I’d like to think that he got a little grin out of it in what really looked like a production line setting that he may have been tired of.
I was lucky enough to talk to Billy Gibbons about Ford Hot-Rods and cancer. He was fuckin’ cool.
Heh. Decades ago, I met Stephen Sondheim. I said (paraphrasing), “I’m not going to go on and on about how you’re my favorite Broadway composer/lyricist, I’m not going to say how I have all your albums, I’m not going on and on about how I’ve always wanted to meet you.”
He replied, deadpan, “That’s exactly what everybody says.”
Not an answer the question, but my father has a friend who knows nothing about modern music, listening only to classical music and not being remotely interested in “pop culture” . Before his retirement he used to be a diplomat in the Dutch foreign service and it was in this role he was in America on a ferry boat. There he got talking to a nice gentleman and they were getting on like a house on fire. What a nice guy, he thought. He looked up to find that crowds of people had gathered. Turned out the man was Johnny Cash. My dad’s friend hadn’t a notion who he was, but we suspect that they had such a good time because not having to go through all the usual chat was refreshing to Johnny.
When I met Geraldo Rivera in the 90s, I simply asked him to sign our petition for whatever that year’s cause was. I can’t remember why he was in the Clearwater Booth, something to do with a new newspaper in Red Bank, NJ I think.
I’ll give him credit, he did sign it.
My father did that with Robert Redford, even asking what he did for a living. (this was at the height of Redford’s popularity, but my father was worse than I am when it comes to pop culture)
Little bit of boasting-- my mother met Pres. Clinton when he actually was president, for some event that involved a library of Slavic literature in the US, and Vaclav Havel was also there. My mother was invited because she was fully fluent in both Czech and Slovak, and also Russian, as a bonus. She had articles in professional journals in Czech, Slovak and English. The fact is, she spoke 8 languages, and read two others. She had a PhD in linguistics.
Anyway, Clinton actually gushed over her, because he found her linguistic accomplishments very impressive.
I talk with celebrities the same as anyone else. Tell them I am flattered but not interested, then increasingly escalate. Hopefully the authorities don’t need to intervene! 