I think you kinda missed the point on this one. He's traumatized from all the rejection he's faced by people that see his erotic art and hear him talk about lewd things, so when Toyoda told him she doesn't want to break up with him and can accept that side of him, it turned those traumatizing words of rejection into playful, even flirty banter. He doesn't like being called gross, he likes being teased specifically by his gf who he now knows without a doubt accepts everything about him.