Why has my father lost his manners of please and thank you? He orders everyone around.

He may feel threatened by his old age and/or any medical conditions he has.   Threat perception can change people in strange ways, and sometimes make them defensive with the need to prove themselves, and/or establish dominance.

Has anyone had a "come to reality" talk with him?  Perhaps he doesn't realize how offensive he is.

You don't mention Dementia but if sudden he could have a Urinary Tract Infection (UTI). This will change his personality somewhat. He may be in early stages of Dementia. Best thing is to get him to the Dr. for a complete evaluation, labs included. Low Potassium will cause problems. Dehydration and diabetes. Thyroid.

what is his ailment? If it is dementia, that area of his brain might have died