This shows just how unnecessary, stupid and unenforceable this rule is.
Here's a scenario.
Two players are tied on the last hole of their club championship match. They're pretty competitive and haven't really liked each other for years. One of them, the one with the long putter, putts, makes it, and apparently wins the match.
His opponent, who is standing to his side, yells immediately--"Hey, that was an illegal stroke. Your hand was touching your chest."
"Was not," says the apparent winner. "Well, maybe it was, just a little bit. But it wasn't intentional. And that's what the rule says it has to be, intentional."
So they storm into the pro shop. You're the pro. What's your decision?
Quickly appoint a rules committee and refer the players to them.
But seriously, in the end, golf is a gentlemen's game, and it would be one player's word against the other. I don't see how the pro could give the match to the complaining player. He has no proof that a breach existed.
In virtually all of the rules, any doubt as to what actually occurred is resolved against the player. Best suggestion get a regular putter and learn how to putt. No longer any doubt.