I'd say you overreacted. I'd have been annoyed too, but I think the responses were perhaps a bit too much. I'm not saying, however, that you had to waste a lot of time, put up with it, or be more kind than they were. Saying "I'm sorry, I'm concentrating on this right now" may have allowed some people to back down - if that didn't work, then perhaps I'd be a bit more stern or sarcastic.

For the LCD comment, you could ask in return, in the same manner the person did, how he could get a good shot looking at a screen instead of at the actual object/area he was photographing. Both questions are stupid, but if he felt his was valid, then reversing the question is just as valid (despite any rationalization on either part).

I agree that using your tripod impressions would not give others a great shot; if they feel they have to use the exact marks, they are probably not good enough to pull it off. Even if you wanted to brush away the impressions, I think doing so _discretely_ without comment would have been better.

That said, I am waiting to make a smart-ass comment regarding how many megapixels my film camera has. If a stranger asks, I will explain things nicely. However, a few men I work with do ask that kind of question, and I know them well enough that I can ask in return "what size shoe do you wear?"