The damage was done, Percy had made up his mind that they wouldn't dance and Katie's description of her dancing skills only solidified his decision. Taking it on the chin and trying hard to fight any resentment - this was an activity he really liked and had hoped to share with Katie. In fact, only a close circle of friends knew that he enjoyed dancing and he was granting her access into a side of himself that not many saw. How could he enjoy himself now, after Katie explained her lack of coordination.
In a very firm, but matter-of-fact sort of way, "Then we shall think of an alternative. Merlin knows that I don't want a black eye to explain away at work, Monday morning. If you don't have any suggestions, perhaps we could go to the cinema? Or... I could simply take you home?"
Percy didn't like that last option, but he honestly couldn't think of anything else.