I usually use this phrase to signal, that deed that the person asking me is trying to perform is really not a good idea for a variety of reasons, while simultan

I usually use this phrase to signal, that deed that the person asking me is trying to perform is really not a good idea for a variety of reasons, while simultaneously I can't think of a single good reason for performing the deed: e.g.: If somebody asked me "how do I go about writing an XML parser for Java", I would firstly respond with the question. And then proceed to explain to our little grasshopper. That ALL the grasshoppers I know have been ignorant enough to go and write their own XML parsers which weren't really good, and made them waste precious life energy (not to mention community's resources) on something they had no business doing. There is a big difference between writing an XML parser for purpose of learning how they work, and writing an XML parser because you are too ignorant to learn how many times before they were already done badly, but still way better than what you will produce. I would also respond with forementioned question if somebody asked me: "How do you go about mending car chassis with duct-tape??". But then I might also ask the question, when faced with a new concept that might be really, really cool. But I was thus far completely unaware of - due to either my own ignorance or lack of experience. In either case - I use the phrase to introduce some humor (or vent some frustration) in an awkward situation.