Is there an actual tag that covers all your blacklisted tags? For example one would search for fav:user + blacklisted_tags and it would show what blacklisted pics he has in his favs. I'm pretty sure there is no such thing but it would be pretty cool.

Such a feature wouldn't really work that well as the blacklist isn't actually processed by the servers during a search (that would be too "expensive" computing-wise) it's actually downloaded and your computer just hides the posts that are applicable to the filter (which is why when you blacklist something broad and widely used like mammal or female you end up with blank pages sometimes—the filter would've applied to all images).

However, being able to subscribe to other blacklists (like how derpibooru handles it) might be a neat idea (and a feasible workaround without having to rewrite the code from scratch).