I regularly host chess evenings, where I and a couple of contemporaries gather to play chess. We listen to (mostly baroque) classical music. Recently, one of the group has started 'conducting' along with the music. I have tried to explain that it is distracting, but they continue to do so, therefore giving themselves an unfair advantage. I don't believe it to be ill intended, but would like that they stop. How can I effectively communicate that their air-conducting is counter productive to maintaining a pleasant evening?
I think you need to phrase your request, not as an objection to the conducting because this could be challenged and made to sound petty; but instead as a request for them to observe the rules and etiquette of chess.
You may find this page interesting as it outlines some "official" and "unofficial" rules of etiquette for chess players. Amongst them are:
• Every game must begin and end with the players shaking hands.
• Between the two handshakes, no talking is permitted. "Check" need not be said. Players are responsible for noticing where all of the pieces on the board are located, and what threats are pending.
• Never do anything to distract any other player in the tournament, especially your opponent.
These would appear to have been written by/for professional chess players, and perhaps for your friendly chess evenings the "no talking" rule might be a little severe; but I think the "air conducting" definitely comes under the rule of not distracting your opponent.
Before the next game begins, perhaps discuss these rules with everybody. You could do this selectively (you pre-select which rules you want to apply, after all it is your event), or you could discuss them in their entirety with the aim of agreeing which should apply at your event to make the game fair but keep the atmosphere friendly and fun.
You could perhaps say:
I found this article on chess rules of etiquette. In professional games the players shake hands and once the game begins they do not speak. Distracting the other player is strictly against the rules. I thought that perhaps the no-speaking rule was rather strict for our evenings, but do we all agree that distracting a player who is thinking about their move is unfair? Could we all avoid any interaction with the background music such as humming or air conducting? I personally find this a little distracting.
This communicates your expectations without picking on one individual and one particular habit. I have assumed that you don't sit in silence for the entire game, but if you do already observe that rule then by all means adjust my suggested approach, but actually I think that would make it easier because people who are taking the game seriously enough to observe the professional rule of no talking would surely be more understanding about complying with the "no-distractions" rule.