Some of them can be guilty, as well. First-time players aside, everyone who plays needs to be reminded to help take care of the greens. Some people don't even look for a ball mark once they reach the green, much less reach in their pockets for a repair tool. They are more concerned with their first putt or their last shot or their last hole or how they look. The condition of the golf course is of secondary concern to this type.
Golf being such a solitary pursuit, it can be awfully self-absorbing.
The very nature of etiquette requires that you develop some common courtesy where your fellow playing companions are concerned. Being cognizant of where they are and how they are playing is as much a part of golf as birdies and bogeys. Your first action upon arriving at the green, once you've hit your shot onto it, should be to look for your ball mark, then repair it. If you want to know how to best help your oblivious friend, you might try humiliation. Point out his or her ball mark.