You want to piss off your opponent, call them on rule 14-2
During league play not long ago I watched golfer B stand directly on the extension of the putting line of golfer A and stand there through the stroke. It was no coincidence that golfer B's putt was on the exact same line. I don't know about you but when I see a rules violation and I strongly suspect the golfer has no idea what he or she is doing (99% of the time) I will not call the penalty but instead try to quietly advise the violator after the hole is complete and then let it go. In any event I called golfer A aside after the infraction and needless to say he had a difficult time believing it is an understatement. "Guys do it all the time". "I see it in tournaments". "I bet I saw it done 20 times during the spring 4 ball". When I advised that he saw a least 20 rules violations I got the "You can't be right, we'll check it in the pro shop after the match."
After the match we met with the golf pro who dutifully looked up the rule. (He could have made the ruling off the top of his head but our PGA professional often times like to whip out the rules book to show us how to use it and to have it open and ready when the whining starts.) Upon hearing the rule golfer A came up just short of stammering, and managed a polite "You were right I'll be darned". But his eyes were a blaze. Not with anger at myself or the rule or the golf professional but with everyone he'd ever seen stand on an extension his partners line. I pity his next opponents if they even get close to an extension their partners putting line.
