you know even if they start off being cranky if you are cordial, polite, respectful and have a good attitude then I have always found they ( the police) are always respectful back.
The one and only time I had a 'bad copper' was due to my mate being drunk in the passenger seat thinking he was gods gift and making a tool of himself which only made for a shitty interaction. Even then though the copper said in a reasonable tone 'get your mate home before he get you (me) in trouble. Your doing the right thing".
When ever I have been pinged I have my licence ready for them before they ask for it and when they do you know? .... if I do I always say i'll cop it on the chin mate.