It is such a Midorima response that Takao can not help himself, he laughs. He would imitate his friend but he won't take the teasing that far because he is truly happy for him. How he feels about Weiss is clear as day to the point guard even from this interaction.

"Shin-chan in love, I didn't know it was possible." He has to get a little teasing in, he would not be him if he didn't.