More Ways to Curate Your Tumblr and AO3 Experiences
I'm probably late to the party on these, but for anyone else who doesn't know, here are a few more ways to avoid shit you don't want to encounter on the above mentioned sites.
I'm pretty sure everyone knows you can block tags on Tumblr, but you can also block words and phrases that show up anywhere in a post, including if said word or phrase is a username, by going to https://www.tumblr.com/settings/account and scrolling down to "Filtered Post Content". So if you want to really avoid anything featuring a particular word or phrase or want to avoid a certain user's posts without blocking them, this is an option. Of course, no shade to blocking people. If you need or want to block someone for any reason, block them. In my experience, this does not block or hide anything that shows up in the notes of a post or in your inbox, messages, or activity, and only functions for URLs that start with tumblr.com (no "username/tumblr.com" type urls). Sucks that this feature isn't as thorough as it could or should be, but it's still been very helpful for me. Further info on Post Content Filtering.
As for Archive of Our Own, you can mute users, which prevents you from seeing their fics in searches or collections or their comments but does not prevent them from viewing or commenting on your fics nor does it prevent you from viewing their profile, collections, or fics via outside links. You can do so by either going to that user's dashboard or profile and clicking "Mute" towards the top of the page or going to "My Preferences" then "Muted Users" and adding their name to your list. Again, please use the block feature as much as you need or desire, but this is also a great tool. Unlike Tumblr's closest equivalent, muting on AO3 is very thorough.
You can also filter out any word, phrase, or username from a search by typing a dash (-) followed by what you want to avoid in the "Search within results" bar.