This song is really ambiguous but my sense is that it is about rejection. In your interactions with someone that you desire but who isn't all that into you might get all sorts of little "nos" (i.e. they might talk to you but won't go out with you or they might go out with you but won't sleep with you, etc.). This song is about the "great big no", the "no" that signals the utter impossibility of anything like a genuine relationship on any level. Once you get the great big no, any further attempts on your part are rightfully considered harassment and/or stalking.
This song is really ambiguous but my sense is that it is about rejection. In your interactions with someone that you desire but who isn't all that into you might get all sorts of little "nos" (i.e. they might talk to you but won't go out with you or they might go out with you but won't sleep with you, etc.). This song is about the "great big no", the "no" that signals the utter impossibility of anything like a genuine relationship on any level. Once you get the great big no, any further attempts on your part are rightfully considered harassment and/or stalking.
[Edit: reworded for clarity]