Not a thank you to a driver, but an interaction I had with one abroad. I was waiting on a platform at Ettlingen Station, south-west Germany, wearing an American blues festival t-shirt, when a train arrived at the same platform. The driver leaned out of his window, and told me he'd recently come back from a holiday in the USA, and we had a brief conversation about holidaying over there, before he set off, giving me a wave, and with big smiles on both our faces. First time I'd ever spoken to a driver!