Unexcusable

If you say that something is unexcusable, you are emphasizing that it cannot be justified or tolerated because it is extremely bad.

The earliest known use of the adjective unexcusable is in the Middle English period (1150—1500). OED's earliest evidence for unexcusable is from around 1384, in Bible (Wycliffite, early version).
unexcusable is formed within English, by derivation.
Etymons: un- prefix1 1b, excusable adj.

Your actions were unexcusable. He said the killing of innocent people was unexcusable.