This comment by @deathcow got me wondering about any run-ins with celebrities that other Sifters have had. With what celebrities have you been been in semi-close proximity and under what circumstances did the encounter take place?

Here's what comes to mind for me, and I'm not including any instances where I went somewhere specifically to see someone (e.g., at a stage show or a book signing):

• I walked around a t-shirt store in the Venetian casino in Las Vegas with Howie Mandel during his Deal or No Deal days.
• I was at the Beverly Center. While just my wife and I were waiting at the elevators to head back down to the garage and leave, Jimmy Kimmel and a couple of his friends stood next to us also waiting for the elevator. He was looking at me over my wife's shoulder as I whispered to her "That's the guy from that talk show," and as she turned around to look he just continued smiling at us like, "Yeah, I know you're talking about me. Go ahead and say hello." But I couldn't bring myself to do it. Finally, more people started coming to wait for the elevator (it took forever) and he walked off as not to get mobbed I guess.
• Looking for parking at South Coast Plaza I saw Kobe Bryant getting into his car after exiting the back door of a baby store with his wife and escorted by mall security.
• At Disneyland I was at the exit of the Matterhorn where Kobe Bryant was getting off the ride and putting his wife up on his shoulders surrounded by a couple dozen screaming fans.
• I've said hello face-to-face with Kobe Bryant on 3 other occasions as he was walking to or from a local cafe next to where I used to have lunch every day. (He lives nearby.) One of those three times I told him something lame like "Bring home that three-peat!" That was after the end of their last back-to-back championship season, obviously.
• I snapped a photo of my wife with Marg Helgenberger (Catherine Willows of CSI) at the end of a Lakers game while heading up the stairs to the exit. She made sure to tell her "You're so beautiful!" to make up for us bothering her for a picture.
• I stood next to Elizabeth Banks at Comic Con pretending not to notice her as she was standing around talking to a couple of friends.

There's something built into me that makes me almost unable to bring myself to speak to a celebrity when I see them. I guess I just don't want to waste their time and be an annoyance, and I know they don't care that I recognize them.