"Can you bring me a pink frilly one?" Bucky asks, grinning at her. "Because I always wanted to walk around just wearing one of those while I made my wife breakfast."

Bucky realizes he said wife and tries to pretend he didn't, hoping that Natasha doesn't catch it or realizes it was just a joke. He does not want any mixed expectations flying around, especially when he'd do something insane like marry the woman on the spot.