I don't mean to be a name-dropper, but: I've had breakfast with Jeff Goldblum, partied with David Cross, and gone grocery shopping with Kate Winslet. Granted, none of these people knew I was with them at the time. They just happened to be in the same time/space as me. So goes life in Los Angeles. Live there for long enough, and you'll have a collection of celebrity sightings as well.
(The Best One: I peed next to Marilyn Manson after a screening of Paranormal Activity 3, and don't think that didn't have a traumatic effect on the 14-year-old inside of me who thought Manson was, quite literally, an agent of the devil.)
The thing about each sighting, however, is that I can recall everything about the event. Jeff Goldblum was at The Griddle in Hollywood, sipping a cappuccino after stirring it neurotically for 20 straight minutes. David Cross was chugging a canned PBR at a house party that was in honor of nearby Silverlake Junction. And Kate Winslet was picking up cheese and bread at a Ralph's in Malibu. I can even remember what I was wearing at the time. These events happened years ago, and I have no problem closing my mind and re-entering their details. In direct opposition to the ease of those recalls, I can't remember what I ate this morning, among other embarrassing memory gaps that drive my partner (among others) into fits of rage.