inexcusable
in-ex-cu-sa-ble
adjective
Too bad to be justified or tolerated; unforgivable.
"His behaviour was inexcusable, and he should apologise."
Thesaurus
Synonyms: insupportable, unwarranted, unjustifiable, indefensible, unwarrantable, unforgivable, unpardonable
Antonyms: excusable