I think I can name the guard concerned, as there is one who has a reputation along the entire east coast mainline (there are others but no one beats the reputation of the one!) He has been known for targeting staff over other passengers. Wether on or off duty if you are not booked, he will charge you, if you are booked, he will find a way to charge you. If you are on boxes, he will find some obscure rule precluding boxes on his train. Unfortunately the tw@t has boxes and so can travel on any train, but woe betide you if you have the decency to ask him for a lift! He does have a tendancy to *ahem* forget.... to fill in a box when used tho.....
He is about to retire. I wont be going to his retirement bash. I have had run ins with him myself!
I believe in looking after each other, as you never know when you may need help, so regardless i welcome ALL rail staff on my trains wether on or off duty, in uniform or not, and i always introduce myself to the traincrew not just out of courtesy, but also so that they know i am on the train if i am needed.