I always assumed that Andy and Barney had to share the squad car for personal use. They even double dated in it. Mayberry County must’ve had pretty lax rules about government property! Either way, Barney says when he walks in that he is there to drive them to the party.
Well, if you wanted to cut in and dance with Romina, and some guy snubs you, would YOU knock him out and then help him? Nooooooot me. Must be the New Doctor wasn't at the shindig.