¿Qué significa I've always been a model citizen
So landing a punch or two- a, "No thank you"

（It's a quote from a lyric）
What is "-a" before "No thank you"？ I want to know this "a" mean.

Could you show me example sentences using this "a"? ?

See a translation

-What do you say? And I don’t want to hear a “sorry, I can’t” or an “I’m busy”!
-Did you hit him with a “no problem, man”? (“Did you hit him with ___?” refers to “did you tell him __?”
-I told him nicely I couldn’t help even though I wanted to and he responded with a “sure”

To land a punch is like a fighting term which means to deal a punch/to hit someone with a punch. In this case it’s probably figurative for giving someone some “punches” (like speaking your mind maybe/saying what you mean)
...a “no thank you” is a continuation of the verb “landing” so “landing a no thank you” (just basically means “telling someone no thank you) This all might be self-explanatory, but I figured I would explain “landing a punch” as well.

I included some example sentences at the beginning of my answer demonstrating how we sometimes use the indefinite article “a” or “an” in front of a phrase (like a direct quote) I hope this helps! Lmk if you have any questions! 😊