Really? IME it can go both ways.
I remember passing my test at 17 and doing handbrake turns late at night in a huge Asda carpark - me in my awesome Citroen AX and my mate in his 206. Probably 1am or so while Asda was shut. Cleaners called the police, single policeman turned up and said he was much happier that we were pratting about off the roads but asked if we could move on. Fine, that's grand, I appreciated that kind of attitude.
On the other hand when I was driving my first modified car at the age of 19 I had no less than 7 producers in the period I was driving it. Not once did I get any points, not once did any of the policemen involved actually have anything to say about my driving or the state of my car, they just pulled me over and gave me some bs about the car looking like it might've been stolen, then gave me a producer.
During this time I encountered a number of policemen that were rude straight off the bat and for entirely no reason. I'm a polite person, I don't lose my temper easily and I'm usually very respectful.. but it's kinda difficult to keep your cool when their opening sentence is "right, for a start, don't open your mouth or I'm gonna get the drug dogs down to check your car out". Had they done that to me now I would've taken their number and filed a formal complaint but at the time it just scared/frustrated me.
That annoyed me immensely and I lost a huge amount of respect for the police then. I was never pulled for speeding - I still have zero points and crashes on my license 5 years later.
All depends on the area and the individual policemen I guess. Coincidentally I was never pulled over by a traffic cop, it was always the standard policemen in their panda cars.