I have several strategies that I use. I am a car driver - have been a hospital car driver for 10 years and am very aware of the problems of poor parking and misuse of disabled bays etc etc. But although I can drive easily I have problems walking and now have a mobility scooter that can be used on road or path - which I call the yellow peril. So I have customized it slightly by having two good mirrors put on it so that I can see what is behind me and also there was the problem of passing people in a civilized way. I wanted something that would alert people to my quiet machine being close to them and yet not a hooter which could sound quite agressive. So I have a good bicycle bell put on it . works a treat. Firstly I am a lecturer and teacher and can say Please with quite a strong tone to it. I begin by simply saying excuse me, then may raise my voice, especially to the zombie telephone watchers , but at the same time I just do a simple ting ting on the bell. that definitely alerts people to my presence and if that does not work I ring it quite a lot more. Regarding the bad parking of cars I also stop and appear to take a photo of the front and back to make it look as though I mean business but in actual fact dont take a photo at all. If they feel guilty they may bluster or just go . If I park in a disabled bay and see another car without a badge in it but a driver there, I politely say excuse me you have forgotten your badge. this can sometimes be the case and they immediately find it and put it on the dashboard. On the occasion where one man was quite rude and said Im only here for a few minutes, I simply replied I suggest you move now. He did not move so I moved my car across the back of him and got out and locked the car. I actually only crossed to the bread shop and came back out. As he blustered about I could not do that etc etc, I replied "Its very annoying when people do things like that isnt it? you were lucky I chose to come back quickly please do not park here again and I have your registration to show the police if I see you again. No doubt one day I will get a black eye but I do not intend to back down from this sort of thing. Sometimes I take another tack and ask in a very soft voice to middle aged men " Is your mother still alive? " To which I get a rather puzzled yes or no and I then ask if they would treat her in the same way as they were treating me and it usually works quite well!!