Whoops, I missed the earlier post about fries + chocolate milkshake. I still think vanilla is the way to go.
But I definitely second the "dont’ knock it till you’ve tried it" opinion.
This is not so different from the commercially successful pretzel and ice cream combos like pretzel ice cream cones and Ben & Jerry’s Chubby Hubby.
Except that whereas pretzels + ice cream = salt + cream + sugar,
fries + milkshake/ice cream = salt + *grease* + cream + sugar – all the better!