In the 2000s, when used in a lawyer-created public apology, a word that demonstrates that the person concerned (eg. a sportsperson) knew their actions would be wrong before they acted, do not regret their actions for one second since, and are annoyed they got caught out and are forced to make a public apology to keep their career going.
When used by another authority such as their coach, using 'unacceptable' implies the latter is also annoyed that the former got caught out, is forced to make a public apology and that the mudsticks to the authority by association.
I realise my use of performance-enhancing drugs to allow me to win games was unacceptable. I would like to unreservedly apologize to the public, my team and my sponsors, for my actions.
Timmy was suspended from school, he brought his Ku Klux Crayons and Colored folk' pencils to art class. His parents are devout white supremacists and purchase socially unacceptable school supplies for their son.
Sally on the other hand brought her Lisa Frank gel-pen and was awarded a horse sticker. She has two fathers and a bowl cut.