|Your manager thinks you need to grow up? His comment is totally inappropriate, and his handling of the parking place shows a lack of understanding of the meaning of workplace commitments, employee motivation, managerial credibility, and fair treatment. This is not merely a matter of what your manager did, but also a matter of how he did it. If it was essential for the special visitors to use the parking spot you earned, your manager should have discussed this with you in advance. At that time, he should have offered an apology and other arrangements at the very least.
The next step depends on how you feel right now. If this matter is not keeping you up at night, you should file it away. However, if it is gnawing away at you, then you should meet with your manager. Open the conversation by telling him that you can obviously handle what happened here, and you have no interest in being given more days in the special spot. Tell him how a last minute change in the ground rules of an important program can undercut employee motivation, morale, and satisfaction. And telling you to "grow up" was insulting. Then ask him what he thinks.
His reaction will help you determine how long you want to stay parked at this company.