I was maybe in junior high when a friend of mine turned me onto squirting ketchup onto mac 'n' cheese. It was glorious. Obviously, tomato-cheese-pasta is a staple in Italian cooking, so it's not like it was a huge stretch. I just had never thought of adding anything to mac 'n' cheese. It was fine straight out of the box.
He said "Well obviously you've added cut-up hot dogs, right?"
A whole new world was opened up, spread before me, and inviting me to try every possibility. Baked beans. Peas. If ketchup, why not a dash of barbeque sauce? Mustard turned out to be a mistake, but hey, it was worth a try. Always see what else is in the fridge.
When my kids were younger, I'd make mac 'n' cheese for lunch sometimes, always adding various things, essentially continuing the experimentation of yesteryear, and one day they asked me if we could just have it plain. They liked it plain, not with all kinds of stuff added (and I
was getting a bit crazy with it, since we have a lot more different things in the fridge these days than when I was a kid).
So I made a double batch of plain Kraft mac 'n' cheese. It was awesome. (I still hit mine with some ketchup though.)