I've seen many in my course of duties, but have spoken to only a few, beyond Tickets please.
Bruce Dickenson (Iron maiden). Was asking about his oyster card. I checked it to see what extra he would need to pay. Was in his pilots uniform.
Eddie Izzard. Asked about the buffet trolley as I checked his ticket from Gatwick to Bexhill. Told him he had 10 mins before it left the train at Lewes and it was in the next coach. He bought something, then changed later onto the Bexhill train at Hampden Park
Frank Skinner: During major delays he had changed trains at Haywards Heath, but left his bag on previous train. Told him who he needed to speak to at Brighton and pointed him in the right direction.
Vince Cable (when in power). Asked about arrival time into Eastbourne. Was sat in Stnd.
Female Doctor Who baddie, head of the Selveene. (did not know her name, just the face). Asked about connections at Hove.
I just try and treat them as normal punters, but at the same time, esp with someone like Bruce D, your brain is screaming, it's Bruce D, aghhhhhhhh.