"Oh, hi!" Baby says to the new person as he comes outside and realizes there's definitely three people instead of two.

And then he sees the car and whimpers a little. He's definitely getting replaced. That car is as old as he is and Dean's going to be all over it and what if Dean doesn't even want Baby as his car anymore?

THIS IS VERY SAD. WHY DOES NOBODY ELSE LOOK SAD? THIS IS CAUSE FOR WORLD-ENDING SADNESS RIGHT HERE.