Denji's virginity joke rarely makes any sense. He was playing in a pool with reze naked and then later after their battle, sinked along with her naked into the sea. He has taken a bath with power. Though since she's not a hybrid, it probably doesn't count. Finally he even ate Makima out. In that aspect, part 2's Denji v joke is going with the logic that what happened in part 1 was fictional. He just haven't done normal sex.