Don't flatter yourselves that friendship authorizes you to say disagreeable things to your intimates. On the contrary, the nearer you come into relation with a person, the more necessary do tact and courtesy become. Oliver Wendell Holmes, Sr.
Any startling piece of work has a subversive element in it, a delicious element often. Subversion is only disagreeable when it manifests in political or social activity. Leonard Cohen
If you have learned how to disagree without being disagreeable, then you have discovered the secrete of getting along - whether it be business, family relations, or life itself. Bernard Meltzer