When it comes to the labyrinthine rules of golf, you never can be too careful. "Here, you'd better have this back in case I get disqualified for not giving your marker back," said Jonathan Davies, the former Wales rugby player, as he tossed a coin to Padraig Harrington.
It may only have been the single-hole putting green in the HSBC Interactive Zone in the Championship Village, but he was right to fess up.
Realistically he had probably already incurred at least a two-stroke penalty for breaking Rule 27 (b) ii: Don't borrow stuff from your playing partner or get on-course coaching.
Had he not called it on himself, anyone could have snitched and rightly made sure he was forcibly ejected from the Emirate.
There have been plenty of grey clouds hovering over the National Course this week. Yet even the most leaden, it seems, has a silver lining.
Harrington's plans for the weekend had initially appeared to be centred on the pursuit of a first Abu Dhabi Championship crown.
They had to be hastily rearranged when his first round 65 was found to have been two strokes short of what it should have been, after he nudged his ball forward after picking up his marker from the putting green. The movement of the ball was so barely perceptible, you needed high-definition television replays to spot it.
When he then did not sign for the right score, a 67 became a DQ, and he was headed for three days of practice instead.
The enforced break gave golf's Mr Tinkerman more time to devote to honing his remodelled game. It also allowed him to give vent to the other thing he says he does well in life, other than "play decent golf" - namely talking.
Yesterday morning, the tournament sponsors handed him a headset and microphone, and he staged a coaching masterclass for three sporting celebrities and a group of children.
Item one on the agenda: how to mark your ball properly. "The first thing is, I'm blaming my caddie for everything that happened," said the Irishman.
Harrington has come a long way since his youth. When he first played for Ireland, aged 15, he only had a half-set of clubs. He had the even numbers and he had to borrow the odds from his brother when he played international matches.
Despite the great wealth he has accrued, commensurate with his success in the game, he said that between him and his caddy, they could only scrabble together a measly one cent coin to mark his ball with on the opening day of this competition.
That is where the trouble started. "The smaller the coin used, the harder it is to mark the golf ball," he said, before running the assembled class through how to place a small, flat object on the grass.
"I line the leading edge of the coin straight down with the back edge of the golf ball," he said, demonstrating the procedure with all the meticulousness of someone who is unlikely to make the same mistake again any time soon.
"If you are looking from the side, you will see there is a tiny bit of room between the coin and the golf ball. Don't put the coin under the ball, because it makes it very difficult to get it out."
Harrington practises everything to a degree that is undoubtedly obsessive compulsive. After running through how to mark a ball, his clinic then touched briefly - by his standards - on how to drop a ball to get the best possible benefit. Within the rules, obviously.
"When you are dropping a golf ball on the course, you want it to go in the best possible lie," he said. "I practise ever year. There's lots of lies you don't want to drop the ball into."
One thing which does come naturally to him, however, is magnanimity.
"I think Padraig has been fantastic in accepting the situation," said the former Scotland rugby player, Gavin Hastings, who was one of the three ex-sportsmen, along with Davies and Chris Cairns, the New Zealander cricketer, in thrall to Harrington.
Complex and, many have argued in this case, unfair.
However, Harrington reiterated that he was happy to take his medicine. "If I was arguing for my life, I would have argued that ball had rolled back into the same hole it had been in at the start.
"But because my reputation is more important than anything else, and the ball really did look like it had moved, so I had to accept it.
"As a professional golfer, your reputation is far more important than anything else.
"The cheque that we win for winning a tournament, my reputation is far more important than that at the end of the day. It looked like it moved, so it moved."