If you don't want a source event to be blocked on your destination calendar, simply add the #nosync hashtag to the Description field of the source event. Here's an example of what it looks like in practice:

Note that others will be able to see the #nosync  in the Description field if they have access to viewing details about your source calendar. Also keep in mind that if you use an "out of office" event, there is no description field so you'll need to place the hashtag on the title instead.