Protocal question on showing hand

[jeffnc]

I was in a hand that was played in an interesting way and it went to showdown but I mucked my set when I saw the winning hand. A player uninvolved in the hand, who I had chatted with briefly earlier, asked me what I had. He commented that he would have asked me before I mucked but he didn't want to appear rude. So now I'd appear rude I suppose if I didn't answer. So technically he could have asked the dealer to show all cards, but I have a few questions.
1) what if a player asks to see all cards, but you throw your cards into the muck in such a way they can't be retrieved. Can you get in some sort of trouble?
2) Is it rude not to answer the question after the hand has been mucked?
3) If you answered, would you tell the truth? If you made something up, what would be your intention in terms of image?