This term, short for "only finals week once," is a parody of the popular phrase YOLO. Originally used as tribal African chant, it has been adopted to refer to an excuse for unhealthy or socially unacceptable actions or habits during the week of college finals, since it is generally accepted that college students will be concerned only with studying or procrastinating, but mostly procrastinating.
Upon realization that finals week occurs twice a year (or once a semester), two variations were added, "OFWOTAY" (ofe-woe-tay) and "OFWOAS" (ofe-wose), but the original OFWO is still acceptable in certain countries.
It has yet to be seen where this phrase will be taken, but considering that it can only be said during two weeks out of the year, it will most likely be overused to the point where hearing it will spark an urge to act violently against the speaker. And if that urge is followed, there is only one thing to say about it: OFWO.
"This is my tenth cappuccino of the day! #OFWO"