I bumped into Dennis on the train, once.
I was on my way to work, and he was on his way to a meeting.
I didn't notice him, at first, because i was reading my book.
He phoned the venue to let them know that he was running late, and told them his name, so my head whipped up.
He didn't notice me do that, because he was picking up all his bits and bobs, ready to get off the train.
He was still banned from Twitter at the time, so (to break the ice), I tapped him on the shoulder, and told him that i missed him on Twitter.
Then, we had a quick chat for a few minutes, before he scuttled off to his meeting, and I scuttled off the work.
I couldn't let the opportunity to talk to him go. He's very tall, and was absolutely lovely.