I met Billy Mills when I was in high school 20+ years ago. He was the guest of honor at a local 5K that very few people ran. My dad talked to him the entire time everyone was racing. I remember Mills being extremely friendly and humble. My dad loved him.
Met Deena on a flight before the 2008 Olympics as I recognized her. You can't really say "how about the weather" when talking to a pro athlete you recognize. We talked running for a while, but I could tell it was one of the thousands of conversations she had had with a fan, so I stopped talking and gave her privacy. She was very friendly though.
I was invited to a dinner with Nick Willis and his wife around 2010. They the most polite, grounded, down-to-earth couple you will ever meet. Nobody there would have known Willis was a professional runner if we didn't already know who we were eating with. Extremely cool guy.
I know these message boards hate on trail runners, but Sage Canaday is another humble, nice, friendly, down to earth guy. I've seen him at several races, run warm-ups or cool downs with him and he'll talk to anyone about anything. He's genuinely a good guy.
Our college team puts on a H.S. XC camp every summer. A couple of years ago our coach got Billy Mills as a guest speaker through a friend of a friend, but kept it a secret.
A bunch of us were sitting around while the kids were in a session on goal setting, and this guy walks up to us and says "you guys look like runners!" And we said something about the team and the camp, and he said "I used to run a little back in the day. Nice to meet you, my name's Billy Mills."
We all jumped up and fangirled a bit, but he was super cool and just chilled and talked running with us. Gave a pretty good talk to the highschoolers too.