Yeah, I kept rewinding it and rewatching it and I still don't get what was so bad about jokingly calling him "boss"...

I think it was just your typical Jim and Pam flirting.

i think pam was just kind of making fun of jim telling her what to do. kind of like when someone tells you to put a coat on you say "all right, mom..."

but why didnt he want them to leave until after they left the parking lot?
so he wouldnt have to see them go off and have fun while he was stuck going to this party?