The Everton soccer club is condemning a group of fans — their OWN fans — after chanting an anti-gay slur at an opposing player … with team brass calling it "unacceptable."

The offensive phrase, "Chelsea Rent Boy," was chanted during Everton's Premier League game against Chelsea at Stamford Bridge in the UK on Thursday.

FYI, "rent boy" is British slang for young male prostitutes who have sex with men.