By random I mean bumping into a celebrity in a place where you weren't expecting to see them, such as an airport, hotel or shopping mall.
You don't have to exchange words with them but you should at least be close enough to make eye contact.
I'll go first. Most of mine are from the UK so not everyone will have heard of them:
Rhys Ifans (actor)
Anna Friel (actress)
Kris Marshall (actor)
Maisie Williams (actress)
Stephen King (horror auteur)
Sharon Davies (Olympic swimmer)
Peter Vaughan (actor)
Graham Hancock (writer, TV Presenter)