In a forum held in the University of the Philippines Diliman on Wednesday, Duterte called out his friend turned bitter rival with insults, the Philstar.com reported.
"I will end drugs, crimes and corruption in six months. My contenders said it's impossible," he said referring to Roxas.
"Bayot kasi kayo kaya hindi ninyo kaya," he added. "Bayot" means homosexual in the Visayan tongue.
The tough-talking mayor also said that he will not be the first to make amends with Roxas whom he believes will fare poorly come voting time.
"I do not want to talk to losers. Maniwala kayo matatalo yan…hindi yan aabot ng number one," he said.
Duterte's fresh tirades came after he recently claimed that Roxas who was then Interior Secretary broke down during the aftermath of super typhoon Yolanda in 2013.
He said that Roxas will not make a good president to lead the country based on his poor performance during the tragedy that took over 6,000 lives.
Roxas earlier dismissed Duterte's antics saying that the personal attacks toward him reflect the kind of platform the mayor envisioned for the country.
The two presidential bets had a go at it last December after they threatened each other with a slapping match that turned into fistfight which ended into a gun duel challenge that was all talk.