To try to convince a friend not to drive after drinking is important and so the <em>way </em><em>to present the suggestion </em>, which is why <em>talking in private will help obtain</em> <em>better results </em>. Another way of showing respect (probably it wouldn't be necessary to talk about their condition) and still caring for a friend is <em>mentioning something that they </em><em>might get interested in staying at the party longer</em>