How I hate

 Perhaps hate is too much of a strong word, but I don't always like when you are trying to write some code and you probably get stuck on a issue you are unable to resolve right there and then, and some smart ass on a forum just turns round and tells you: "Why are you re-inventing the wheel?  Just use this or use that."

The whole point of "re-inventing" the wheel is to learn.  I mean there are quite a few open-source applications that can probably do almost everything you want, but some do require that you go through a steep learning curve so as to learn that application.  Personally, I do prefer to write everything from scratch.  Its more fun and since its my own code, it will be a lot easier for me to fix any bugs that I may encounter.