I hate having to either memorize peoples name, write em down on note pad/word, or adding them to my friends list with a very rude/negative comment about them. I usually make alot of friends on the game, but alot of times my active black list takes too many slots of my friends list. I will occasionally go through and delete inactive black listees but that still dosent cut it. the black list should be a seprate tab in the social panel and when a person on your black list joins they NEED to get a message such as "you are currently black listed from such and such and may not join this group" (for pug purposes) this will 1 show a player who is black listed by the majority of the server (which on my server there are alot of groups with mutal black listees) 2. hopefully impact them enough to switch servers, quit (most likely choice) or be a better player/person to be likable enough to group up with.
OR
(and for god sakes read the OR option and dont choose to be a selective reader)
or when a blacklisted person tries to join your group, and your group lead, then there will be a change of color in their name or a symbol indicating their a black listee in chat or a join request.