Ad Dlo Yoda means you are so stone drunk, you dont know the blazing difference between Arrur Haman and Baruch Mordechai. That means highly intoxicated.
And you are obligated to reach that state on Purim.
(Some people look for an excuse to not get drunk, so they might pick and choose a more kula’dik opinion that allows them to not get drunk, even though Shulchan Aruch says to get drunk.)