"He who excuses himself accuses himself. (Qui s'excuse, s'accuse)" - Gabriel Meurier, Trésor des sentences

"Apology is only egotism wrong side out." - OLIVER WENDELL HOLMES, SR., The Professor at the Breakfast-Table

"And oftentimes excusing of a fault
Doth make the fault the worse by the excuse."
- SHAKESPEARE, King John

"Two wrongs don't make a right, but they make a good excuse." - THOMAS SZASZ, The Second Sin

"It is a good rule in life never to apologize. The right sort of people do not want apologies, and the wrong sort take a mean advantage of them." - P.G. WODEHOUSE, The Man Upstairs