I no longer smoke and respect the choice of those that do, however when I step off the train for a "fresh air" break I really don't want to inhale your smoke, so please move far enough away from the door (staying in sight of car attendant/conductor so you can hear and see when it is time to re-board) and judge the wind direction so your smoke doesn't blow on those entering or exiting the train.
Yeah, this is one of the things that bothers me most about traveling on Amtrak. After breathing cooped up air for a day or two, I'd like to get off the train and get some fresh air. You get far enough away from the train to get away from the diesel fumes... and end up with the smokers. It would be nice if Amtrak designated a smoking spot for every train and stop, so everybody knew where to go. For example, smokers are always at the front of the train, nonsmokers near the back, or something like that.