Jordan, I think it would be normal to take off you jacket when bowling. A jacket might hamper arm movement. Personally, for that casual of an event, I would forgo the jacket altogether, unless you need it for warmth when you are outside. A waistcoat, will give the open shirt enough style that you won't need a jacket. You don't actually say, but I am assuming that you will be wearing a kilt with your waistcoat and open shirt. Kilted bowling -- I'll bet the women will enjoy watching you bowl!