Inexcusable (adjective)

Not able to be excused or justified; unjustifiable;unforgivable.

Origin:

From in- ("not") + excusable.

Examples:

1. His behavior was inexcusable and he was fired from the company.
2. The mistake was inexcusable and resulted in a loss of money.
3. Her actions were inexcusable and she was banned from the organization.
4. The delay was inexcusable and caused major inconvenience.
5. The error was inexcusable and resulted in a loss of data.