Pedantic is not a common word. It means to be disapproving, specifically by correcting small errors and giving too much attention to minor details. A more common adjective is nitpicking. Another way to say this phrase is: "Stop nitpicking." OR "Give me a break!"

I think "spare me" means don't cause me pain/suffering. So - don't cause me pain with your pedantry. Spare me your excuses. (I've heard them all before, I don't need them). Spare me! = don't kill me

"Pedantic" means in the manner of a teacher, especially one who likes to follow rules. If you say someone is pedantic, it means he talks in a way that is intended to instruct. It is often used in a critical way, sometimes even as an insult, so "pedantic" doesn't just mean "like a teacher". Instead, it means "TOO MUCH like a teacher". "Spare me your pedantic ways" means "stop being pedantic". It is an insult.

"Spare me your pedantic ways." To paraphrase this, you can say, "Don't be so nitpicking" / "Don't be such a perfectionist" / "Don't be so finicky" / "Don't be so fastidious". EXAMPLE: I once had a really awful teacher on italki. He was so pedantic. He jumped at every little mistake that I made, never letting me finish a single sentence. Needless to say, I dropped him after just one lesson.