Famous for, like, serious grown-up things? John McCain, then a Senator, spoke at my college commencement. We shook hands. I was surprised several years later when I saw him on the news running for POTUS. Politically, I am not a fan, but the man who spoke at my graduation ceremony seemed cogent and reasonably witty. A few years later, not so much.
Famous for, like, well-known TV things? I’ve been manhandled by Misha Collins. A friend and I went to a convention in Las Vegas, and decided to go for a photo op. She’s very shy and wanted me to do all the talking, so when we got to the front of the line, I stepped up and introduced her, and then introduced me and told them I was afraid of nothing. “Nothing?” says Misha. “Nothing,” I answer. I was promptly grabbed by the braid and spun around. We got a picture where my friend and Jensen Ackles were on one side, looking like totally normal humans posing for a photo, and on the other I’m being tipped backwards, held hostage by my hair, while Jared Padalecki pretended to eat my face. It’s on tumblr somewhere.
Famous for, like, intellectual things? I had a nice conversation with David Brin once at an academic conference. I had no idea who he was at the time. He was involved somehow in my instructor’s pet project, I think.
Famous in other countries? The same friend from above had been on several previous trips to Las Vegas with me, mainly to see foreign bands play in small venues at reasonable prices. The Hard Rock Casino has a “club” called Wasted Space, about the size of two postage stamps and a bar, in which we saw a Japanese band called VAMPS. It’s a side project of a guy named Hyde, otherwise known as vocalist for a band called L~Arc~en~Ciel, who hold the record for selling out the 50k seat Tokyo Dome arena – under five minutes – for one of their anniversary concerts. I managed to shove my way to the front of the crowd. Hyde is very fond of standing right on the edge of the apron and letting the fangirls paw away with impunity. 
Famous for, like, internet geek things? I just recently discovered that I know Mookie, of webcomic fame. I’ve known him for months, in fact, but I met him in a group of local performers who took months to remember to go from his stage name to “Michael”, much less tell me what his last name was. The last time I saw him in person, he was shirtless and covered in fake blood, and his very pregnant wife was standing behind him in her underwear, looming and carrying a chalice. (It made sense in context. Hilarious sense.) I had no idea until I saw one of them tag him on Facebook by his real name, and noticed he was putting out the second Dominic Deegan omnibus.
ETA: Oh, and a few months ago I was within about a foot of Johnny Weir. The Jimmy Fund people put on a charity showcase every year, and a surprising number of high-ranking figure skaters were willing to donate their time this year. Kimmie Meisner was there as well, but Weir made it a point to skate wide around the edge of the arena and make eye contact with people. I bought a front row seat for something like $30. He’s tiny in person, but you don’t notice until he’s standing next to a young lady you happen to know is five-foot nothing – he has enough personality for three or four people, even before the attention-grabbing outfits.