Disable taxonomy terms in certain contexts or split into different vocabularies?
Alternative 1
Create two different taxonomy vocabularies:

Events
Users

since the use cases for each are different.
To create another taxonomy vocabulary easy and fast, you could export your existing terms and then import them into a new vocabulary. This could be done with some taxonomy bulk import/export module, maybe with https://www.drupal.org/project/taxonomy_csv or with https://www.drupal.org/project/taxonomy_manager
Alternative 2
Added to this answer after OP's first comment.

Keep the Events and Users together in one vocabulary, EventsUsers.

Create another vocabulary, EventUserType. Add two terms:
Events and Users.

Add a Term reference field with Check boxes/radio buttons to the EventsUsers, save. In the next
configuration pages choose vocabulary EventUserType. Also change the Number of values
from 1 to Unlimited.


Now all the terms in the main vocabulary can be tagged as Event, User or both.

The filtering could be done using the Views module, but I guess that would be a separate question here on Drupal Answers.