AITA for my response when asked "why are you still single"?

As relationship expert Dr. Terri Givens explains, 'Boundaries are not about controlling other people; they are about clearly communicating what is acceptable and what is not acceptable in your interactions with them.'

The OP is experiencing a common conflict where societal expectations (that single, successful women must provide a reason for their status) clash with the deeply personal right to privacy. Her initial responses were ineffective because they were reactive and still engaged with the premise of the question. The shift to a provocative, boundary-testing remark—though rooted in a desire for power—is an extreme reaction to feeling persistently violated and pitied. This action successfully stopped the immediate line of questioning but did so by introducing shock and conflict, as seen in the sister's reaction and the boyfriend's expectation of an apology.

While the OP's underlying need to enforce a boundary is valid, the method used (the 'slutty' tone and 'duck face') was inappropriate for maintaining positive long-term relationships with family and acquaintances. A more constructive approach would involve establishing a firm, non-emotional script beforehand, such as, 'I appreciate your concern, but my relationship status is not something I discuss,' delivered calmly. This maintains dignity while clearly signaling that the topic is closed without creating unnecessary relational drama.