没有公主命却得了公主病
[méi yŏu gōng zhŭ mìng què dé le gōng zhŭ bìng]
This nickname means 'I do not have the destiny of a princess but I've caught the disease of princess-ness.' This suggests the person doesn't have royal background or special privilege (destiny of princess), yet acts or feels like she is overly entitled or precious without justification.