Robert F. Kennedy Jr. sounds like a bizarro Dr. Doolittle ... because he once chopped off a dead raccoon's penis.

President Trump's Secretary of Health and Human Services has a new biography out, written by Isabel Vincent, containing a journal entry of him recalling a strange interaction with some roadkill.

In "RFK Jr.: The Fall and Rise," there's a passage from RFK Jr.'s journal that reads ... "I was standing in front of my parked car on I-684 cutting the penis out of a road killed raccoon, thinking about how weird some of my family members have turned out to be."

Yes ... RFK Jr.'s brother Douglas Kennedy and cousin Bobby Shriver are the family weirdos.

Anyways, RFK Jr. had his kids in the car patiently waiting as he chopped off the raccoon's sexual organs for further study.

RFK Jr. is going for the hat trick here ... he's also had some strange encounters with a dead bear and a dead whale.