If the question is about a topic that's been discussed many times, then a polite suggestion to use the search function (with maybe some advice about key words to include or how to make the search more selective) is a good way to respond.
Just posting "DO A SEARCH, NOOB!!! This topic has been done to death!" doesn't really help much.
Exactly ... the problem isn't the suggestion to do a search, the problem is when someone yells (uses caps) at someone in a rude way to do one and is nasty.

