Formal:
* The company's response to the customer complaint was unacceptable and demonstrated a lack of care for their clients.
* The level of violence in the video game is unacceptable for children.
* The candidate's stance on immigration is unacceptable to many voters.
Informal:
* It's unacceptable that you forgot my birthday!
* The state of the kitchen after the party was unacceptable.
* The quality of the food was unacceptable for the price.
With Emphasis:
* This behavior is simply unacceptable and will not be tolerated.
* The decision to close the school is utterly unacceptable and must be reversed.
* The delay in delivering the package is totally unacceptable and needs to be addressed immediately.