Upon leaving a mourner (when one visits him / her during shiva), one says:
המקום ינחם אתכם בתוך שאר אבילי ציון וירושלים
"May G-d comfort you among the mourners of Zion and Jerusalem"
Since during Tish'a B'av, we are ALL mourners of Zion and Jerusalem, would or should we say this to any / everyone we meet?
I have not seen this done, so perhaps this is inappropriate or maybe there is some other reason why this is not commonly done. If this IS done, who / what group of people have this minhag?