Steve laughs a little. Not at Tony mind you. It just brings up some nice memories. "I did celebrate pi day." He thinks it was an excuse for Natasha to eat pie with him, but it works. Besides, he just really likes the subject in general. How does Tony think he developed his fighting style with the shield??
Anyways, Steve nods. "Have you ever sang the pi song? It's a lot of fun." He still to this day has no idea why Baker's Square didn't kick him and Natasha out for playing the Youtube video while stuffing their faces.