被偏爱都有恃无恐

This means 'When being favored, act presumptuously'. This could imply the person has received so much attention or favor, that they feel emboldened to do or say things freely, confident of the other side's continued acceptance or indulgence. In another sense, they take advantage of the fact that they're special or preferred by someone or something, and therefore have the confidence to express or act more liberally.