My partner drove me and a friend out for dinner (so we would be able to have a glass of wine with dinner)
We were driving on a long stretch of road where there are fairly recent (less than a year) speed cameras.
I could see that he was driving at 56 and the limit is 50. So I quickly said slow down because there are speed cameras. He snapped back that yes he knew, I then said the speed is 50 and he again snapped back with - yes I know and that's just the average speed anyway so stop being an annoying backseat driver.
There was an awkward silence. Think my friend felt uncomfortable.
I tend not to ever comment if someone else is driving as it can be annoying, but felt I should say something as I wouldn't want him to get points or a fine.