So, he hasn't bumped into Ianto yet today and Ianto's neglected to call him to advise him of the latest development in their three-way relationship, and so he has no idea of Spike's transformation today. But it is about time he talked to Spike, given the content of their last dialogue, and so he heads across to the Blood Shack, completely unsuspecting of what he'll walk in on.
...He stops and stares. No question who the blonde behind the bar is, and the surprise rapidly turns into a leer.