Fries and mayo are delicious.
Then again, it could be a throwback to when I lived in Germany. It is delicious regardless and I pity the foo' who doesn't like it.
If you haven't tried it, be quiet and actually try it before badmouthing it. Personal experience dictates it works better on squishy fries like crinkle cut or steak fries.
As for ketchup, limited uses here. Sandwiches/fries maybe (if I don't feel in a mayo mood). Never spaghetti, that's just blasphemy to my boyfriend's cooking.