An erect penis that is beyond large, beyond thick, beyond long, beyond extra-long, and which stuns the (lucky?) looker-on. Unusual shapes figure into the formula too, such as a very long thick shaft with a very small glans (head). The judgment as to whether a penis is a freak of nature
is somewhat subjective, although there's a consensus that a true freak of nature doesn't look quite normal, no matter how impressive it may be.
"I saw an Al Parker movie once. Man, was he a freak of nature!"
"Yeah, I could never reconcile that size dick with that size body. But even though Parker was huge, he wasn't freak-of-nature huge by size alone. He was rather small in body, and it's the discrepancy between Al and Al's erection that made him look rather, um, unworldly."
Harry (or "Hairy") Homo was a mean way to refer to the late Perry Como, a talented singer who was none of those things.
"Karen! Come quick! The Harry Homo hour is just starting!"