If Outlook 2016 keeps asking you to activate over and over, The following should fix the issue:
1. Go to KeyChain Access.
2. Search "Exchange" under Login --> All Items and delete everything.
3. Search "Office" and delete everything.
4. Search "ADAL" and delete everything.
5. Launch Outlook.
6. You will get the activation prompt and the if account is already added, you will see the password prompt for app and ADAL again. You should be able to activate now without it looping.