THIS is an occasional series in which we have a little whinge about things that assail Keeping Posted along life's way. Readers are welcome to contribute their own moans and groans for inclusion. MTR drivers of connecting trains who consistently shut their doors just as commuters spill out of the train on the adjoining platform and head towards it. (MTR chairman Hamish Mathers, please note). Meaningless police roadblocks, especially at the entrance to the Cross Harbour Tunnel, which cause endless jams and needless aggravation to motorists - while, no doubt, providing the boys in blue (with nothing better to do) much fun. The much-hyped introduction by restaurants of a new word - grazing - to the culinary vocabulary to indicate meals at which one can pick and choose from a range of dishes. What was wrong with the old word used to describe just such a meal - buffet? Lawyers whose standard line when defending teenage robbers in court is: ''He comes from a broken home.'' Still no reason to break into someone else's home, is it?