I'm pretty sure '/ac "Physick" <mo>' has never targeted myself accidentally unless the macro had a second <me> line in it or I made a mistake. I don't think <mo> defaults to self with no target like <t> does either. There is a 'click on self' setting that enables/disables clicking or <mo> on your own character. Are you sure that is not enabled and you are not accidentally mousing your nameplate?