So, a Dirty Wastelander is two parts whiskey, one part Nuka Cola, and one part Mutfruit. If I was planning on making this drink in real life, what would the closest tasting thing to Mutfruit juice? Graqefruit?

I would guess closer to an apple.

From the Wiki:

Doya think "mutfruit" may of been a horribly overlooked typo and it was ment to be called "nutfruit"? I know it was spelt the same in NV but Bethesda probably thought "ah screw it, no one noticed".

I only say because it looks a bit like a bunch of weird mutated plums to me. And wastelanders would call it a nutfruit because it's a big fruit with what appears to be a nut in it.