I must have synced too many times because I see duplicate events on my iPhone/Mac how do I fix that?

Here's what you can do:

 

1)  open up your Calendar application

2) In the upper left click "Calendars" (see red circle be 

) to open your list of calendar subscriptions

3)  On the calendar subscription you want to delete - Right click or double click (depending on your settings) to open the options menu

4)  Select the delete option