With a tight, self satisfied smile, he trotted over in his bare feet across the tiles, snatching his mobile along the way from the railing. Then leaning close against Missy, holding the phone at arm's length, he told her, "Smile!' as he flashed his teeth, while the camera built in the phone flashed.
The Doctor wanted photographic evidence when the Master changed back, because there was the possibility he wouldn't remember what happened.
"Go. I picked one out for you, it's hanging in the first changing room." It was selected as a joke, and Missy didn't have to wear that one, but the Doctor thought it was funny. As he waited, he sipped from his own drink, a coconut, fruity concoction.