Sometimes, if a rhetorical question is asked snarkily in my earshot, I feel like giving a sincere answer. I don't, though, because I wonder if it would be too rude (or rhetorical rudeness).
Situation that happened today:
I went to the dollar store. There were two boys (maybe 12-14ish) standing outside selling apples to fundraise for... something. As I went into the store, they asked if I would buy an apple to support their cause. I declined with a smile and said "Sorry, not today. Good luck, though."
They were asking every single customer who went into the store. At least, on my way through the parking lot and into the store, I saw them stop every single customer (about 6 people) on their way in.
As I left the store (less than 10 minutes later) the same boy to ask me the first time asked me again. So I answered "Sorry, you already asked me. I'm still not interested. Good luck." Again, with the smile.
The boy made a face at me and then turned to the other boy and said (quite loud enough to be heard by everyone around, including me) "{Diety}, how are we supposed to know if some stupid {ahem} was asked or not."
I kept walking, but what I really wanted to do was turn around and answer with a smile. "Well, if you ask everyone going into the store, then you've probably already asked anyone who comes out." There's only one door in/out of the store. They were standing by it.
Would that have been rude?