"This is just demo code" is not an excuse

Many, many times, I've seen and heard people show code for the purpose of demonstrating something.

To allow them to focus on a specific aspect they may do some things in a sub-optimal way or a way that makes future maintenance of that code harder.

Sadly, it's common for such demonstrations to be accompanied by the disclaimer that "this is just demo code and you shouldn't write code like this in real projects." 

Technically, such disclaimers are good, but they're worthless if there is no separate example of what good looks like. (Ideally, the person giving the demonstration will point to such examples.)

If all the code people ever see is "demo quality" and not what "should" go in a robust, production-quality code base, that's all they'll ever write.

This also applies to overall maintainability.

If parts of a codebase are over-simplified/neglected/mistreated/obscured to give prominence to the particular aspect being demonstrated, it can be easy for people to think that the maintainability of ALL code isn't important, and so they start writing code like that too.

Please don't give such demos.
And, please, call me out if you ever see me doing this.