i shall see you in the next life

Maleficent is certainly someone you wouldn’t want at a party, but she’s also someone powerful enough that only a fool would ever dare treat her with such blatant disrespect. The only way the King and Queen could possibly have gotten away with not inviting Maleficent was to not invite any of the fairies at all; inviting the other fairies and excluding her is explicitly taking sides in the conflict between the fairy factions.

Which means they made themselves her sworn enemies, and she responded by treating them as such from then on. If you actually get into analyzing the social dynamics of the scene, it’s very clear that Maleficent was willing to show mercy at first by giving the King and Queen a chance to apologize for their disrespect to her. She doesn’t curse Aurora until after she gives them that chance and they throw it back in her face with further disrespect.