That's Devin Haney ripping Vasiliy Lomachenko and his team days after winning a controversial decision against the future Hall of Famer in Las Vegas ... a fight many fans believe Loma should've won.

ICYMI, Haney won via unanimous decision ... with two judges scoring 115-113 (7 rounds to 5) and another giving it 116-112 (8 rounds to 4).

While the fight was razer close, Loma's team believes he clearly won ... and they wrote a letter ripping the judging for what was a fantastic night of boxing.

"Loma was denied this victory in the ring on Saturday," Vasiliy's manager Egis Klimas wrote. "He deserves the opportunity to be ranked #1 and to get another chance at realizing his goals as soon as possible."

Haney, the undisputed lightweight champ, caught wind of what Klimas said ... and he responded, using harsh words, and a photo of Loma crying after the fight.

"This guy is a f***ing sore loser," the 24-year-old said on Twitter. "Get this privilege sore loser out of boxing he makes excuses as he goes!"

"Take your lost like a man & stop crying.. it was set up for you to win for the 3rd time in your career & you failed!"

Haney (30-0, 15 KOs) also seemingly revealed that he was fined for pushing Lomachenko at weigh-ins ... and it was a 6-figures!!!

"Tell the commission to give me my 400k back for that push!" Haney demanded.