Ehhh, it depends on your expectations (or how you "mentally deliver" it, for a text joke). To me just a prison rape reference is kind of tired, so spelling it out contradicted my expectations and was much funnier.
Ah, I hadn't considered that reading of it. For what it's worth, I'd want a full stop period or even line break before the second punchline before I'd read it that way. In that way the joke is perhaps much more funny to people who read it that way and only slightly less funny to others.
