"Do you know who I am?"
possible replies;
"Ask nurse, she'll tell you"
"We've got one here can't remember who he is Sergeant"
"Perhaps there's a piece of paper in your wallet with it written on?"
depending on circumstances.
I'd have just said in a very loud voice to the person next to me;
"This man keeps kicking me and I have a bad ankle. Woudl you mind dreadfully swapping places, perhaps he'd be less inclined to kick you?"
I've been on trains with small children, though, you lose your sense of embarassment quiet quickly fending off endless questions/statements about your fellow travellers "That man's got a wig on hasn't he Daddy?"