According to the master chuuni Kiryuu Hajime, the chuunibyou affected need also people who don't understand them. We could thus deduce Hatoko not understanding a shit Andou was talking about might not have been such a big deal for Andou himself. It only became a deal of any sort after that outburst and Hatoko disappearing. This might explain why he put no effort in trying to teach Hatoko. He could have even been enjoying the feeling of appearing unexplainable in a friend's eyes, especially since he clearly had no idea Hatoko was in love with him and was suffering because she couldn't get a thing out of his nonsense.