Bringing coffee in is a power move if you’re employed already. It says “my time is just as valuable as yours and I intend to make the most of it regardless of what you think.” As someone who just interviews to keep his skills sharp at this point, it’s not the worst thing you can do so long as you don’t make a big deal out of it.

I’d be more offended if they require you to prepare a slide deck of some useless example you probably made up anyway. That’s working for free and I won’t do it.