to be full of oneself, to act high and mighty
Desde que foi promovida, ela anda com o rei na barriga.
Since she got promoted, she's been acting high and mighty.
The expression comes from the age of monarchy. When a queen — or a royal favourite — was pregnant by the king, she was treated with special deference, since she might secure the dynasty and an heir to the throne. To "have the king in one's belly" literally described that privileged condition.
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