Credits: CARMINE MARINELLI/QMI AGENCY
The on-again, off-again couple were arguing on the commute to work, and the woman pushed her boyfriend's head. He responded by biting off her thumb, Florida Today reported.
"He bit it completely off and spit it out on the floorboard," a spokeswoman for the Palm Bay, Fla., police told the paper.
Police said he has confessed to the attack.
The woman was treated at the hospital, but doctors were unable to re-attach her thumb.
Her boyfriend has been charged with aggravated battery.
He is being held in a clear-walled cell that allows for constant supervision of inmates who police think may harm themselves, the paper said, or who haven't been cleared by mental-health staff.