I wish I could take the credit for this brilliant analogy, but I can’t.

CJD is just like the underpants gnomes*.

Step 1) ingest protein
Step 2) …
Step 3) profit!

Explanation:
Creutzfeld-Jakob Disease
South Park’s Underpants Gnomes

For more particularly interesting reading on prion diseases, how you get them, and why you should never, ever eat Haggis, see this and this.

*Before I get reamed for being crass and heartless, I should point out that this analogy is about our understanding of the disease process, and not what it’s like to get it.