If you come across a Guard who gives you attitude for knocking on his cab door, tell his TOC! I get deeply irritated when certain colleagues take the attitude that they will deal with the perpetual annoyance that is passengers when they feel like it and not before, if they feel like it at all. As though they are doing everybody a favour by going out there and doing tickets, or bothering to pick up the PA and make an announcement of more than two words!
We are on the train for you, the passenger, as well as to carry out various other duties relating to safety and the running of the train. There are times when we are busy, sometimes this will be obvious and sometimes it might not be, but there are few instances where we are so busy that we cannot possibly show our face in the train for the whole journey. Sometimes the train is big and we can't get through all of it, or there is a stop every few minutes, or we are jam packed. But if you've made the effort to find us then you should at least be able to expect some courtesy! If we are in the process of dispatching a train, or - my pet hate - clearly in the middle of making an announcement (!) then it is not helpful to be tugging on our sleeve because you require a ticket. However, we all have a tongue and can politely ask you to wait a moment. If we cannot do tickets at all, we have a PA system with which we should inform you (but we ought to still come through the train). The same applies if we are going to be 'unavailable' for some time due to some other pressing need, for example the oft-mentioned 'safety duties', it takes just a few seconds to tell people what is happening and where you can be found if you are needed. I'm not the perfect Guard by any means, but in this age of quick fire prosecutions and sky-high fares, I do sympathise with the passenger who wants to buy a ticket, or just expects to see the Guard who's wages he is contributing towards!
It's our job, don't be afraid to ask us to do it!