I prefer JDM for Jeff, mainly because I got into this fandom through college fics in which often Jared's brother played the part of Jensen's roommate or best bud. To avoid confusion I will always use JDM or Jeffrey Dean Morgan in full:)

I thought the combo-names were already floating around on LJ and other fan hangouts before Tumblr got popular, but either way that's a stupid reason for silly names. *huffs*