These types of cards can be used in any situation, no matter how petty, to let a person know how you much you hate them or something they did.
“Have a previous boss that treated you like dog crap. Send them a fuck you card with a personalized voice recorded message letting them know how big a piece of shit they really are.”
“Did an old boyfriend or girlfriend cheat on you? Why not send them a fuck you card wishing an STD upon them.”