First of all, bitter olive oil is not acidic or spoiled. Oil acids are not bitter but sour instead. Therefore, oils don’t get bitter while they go bad. They go sour instead. Bitterness comes from polyphenols which show that olive oil is good.
If an olive oil stings your throat and tongue it shows that it is earl harvest. This means the olive oil is preserved well on contrary to being spoiled. Good olive oil leaves your mouth clean and fresh. If it makes your mouth feel oily that means olive oil is old and was left open.