It's bad to burn bridges.
Neil has already given his two week notice two weeks ago and it's his last day on the job.
Neil wants to say goodbye to his manager.
Neil tells his manager bye that he wishes him well in his future and that he hopes they run into each other someday.
Neil tells his manager bye, that he's an awful person and that he's so glad to never work with him again.
The manager is happy to hear Neil hope they see each other again and is ready to give Neil a reference for a new job.
The manager is shocked and insulted that Neil thinks of him like that and vows to never give Neil a reference for a new job.