Familiar, colloquial form of あなた. Often considered rude or overly casual when used with strangers, superiors, or in formal settings. Common among close friends, family, or in rough speech.
See also: あなた
あんた、何言ってるの？
What are you talking about?
It's your fault we're late, isn't it?
君 is a casual 'you' often used by men toward equals or juniors, whereas あんた can sound blunter and is used by both sexes.
あなた is the neutral, polite form of 'you', while あんた is its casual, blunt contraction used with close friends or in rough speech.
Contracted from あなた (anata). The shift from 'a-na-ta' to 'a-n-ta' is a common colloquial reduction.