
How selfish, stupid, ungrateful, etc. can you get?
Expression of Disbelief
Used to express shock or disbelief at someone's extremely bad behavior.

You missed your best friend's wedding for a concert? How selfish can you get?
Rhetorical Question
It's a rhetorical question, not expecting a real answer, but to emphasize the point.

He always takes the largest piece of cake. How greedy can you get?
Stress and Intonation
Emphasis is often on 'how' and the adjective, reflecting disbelief or criticism.

She never thanked you for your help? How ungrateful can you get?
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