i have had experience that someone said "This has been answered before" but the truth is that existing threads revolves around similar topic but is not the same. but there are also occasions that it is actually answered before and the keyword to search and the answer that follows are direct, straightforward and easy to understand in the first few links, so what some other raised are not unreasonable as well.
i think there is still a difference of how things are phrased. the same meaning can be phrased it in a rude manner or a neutral manner.
"Can't you google it?" - rude
"This has been answered before, go search for it." - authoritative
"This has been answered before. you can search for it." - neutral
"google is your best friend" - neutral, but redundant.