I think the best thing to do is to sit down and come up with a list of parts of the app that need to be touched to complete what they are asking for. When you lay it all out, even at a skeletal level, clearly there are a lot of moving parts right? We sometimes get the taunt that "oh come on, it's only another if statement", but besides the shit code and maintenance nightmare that kind of thinking/implementation causes, when we lay it out for a few minutes the complexity becomes apparent - add a column to the database here - oh crap that migration will take 20 minutes to run - oh crap, we need to make sure that field is going to be indexed properly, create the frontend to modify it - oh crap, it has to work for the clients still using IE6?, oh crap! they need it to print nicely too? etc...

There's no need for anger or to become irate - it's a matter of education. I'm sure there's many a HN reader who has poo-pooed non-technical business types for the perceived easiness of their jobs, and for some posers it's deserved, but you don't really know that until you take the time to understand the other person's reality.