Not that dont agree with your suggestion, but are you aware that blacklisting wont prevent you from getting paired with them through DF again?
Even if you do blacklist them, it wont make sure that you never see them again, it will "only" prevent you from seeing anything they write in chat, prevent you from joining their PF-parties and them from joining PFs you created (they can still join PFs that you joined aswell though).

If blacklisting people would actually make sure that you "never see them again", aka never be paired with them through DF again, it would make the whole match making system way to complicated (seeing how every person in a 4-man-party can have 200 people blacklisted and how stuff can snowball from there).
So, while its generally not a bad suggestion, I'm not sure if it would actually accomplish what you're looking for.