Last weekend, Liverpool condemned their fans singing the 'rent boy' chant at Billy Gilmour.
The 'Chelsea rent boys' jab is actually decades old: it's believed to have originated in the 1980s.
Here is a quick explainer on what it means, how it came to be and why it's offensive to gay people.
What rent boy means
'Rent boy' is a colloquial expression to denote a male prostitute. 'Rent boys' are usually young gay males catering for older clients.
1980s origins
It appears the song has originated in the 1980s when police found a Chelsea hooligan having sex with a 'rent boy'
At that time, rivals fans used to sing a 'Chelsea aggro' chant at the Blues fans, and after newspapers reported the incident, they replaced the word 'aggro' with 'rent boys' in order to mock Chelsea fans.
Another explanation is that the Stamford Bridge stadium is located next to Earl's Court, an area with plenty of sex workers back in the 1980s.
The chant has become so ever-present so some rival fans see it as a traditional anti-Chelsea chant, which makes stamping it out even more difficult.
Curiously, there are accounts of Blues fans singing the chant about themselves, appropriating the term
However, the 'rent boys' song has somewhat changed its meaning in recent years, with rivals fans now using it to target Chelsea players, not Chelsea fans.
Mercenary claim
When Roman Abramovich bought Chelsea, he invested a lot of money in the club, which has resulted in the perception of the Blues as a 'money-bag club'.
For rival fans, players who decide to move to the Bridge do it because of money, not because of the club's history and appeal, as is believed to be the case with the likes of Man United, Liverpool and Arsenal.
In minds of rival fans, only 'mercenaries' would join Chelsea—and hence the term 'rent boys' could be applied for these players who supposedly sell themselves out for money.
Loan system
In the 2010s, Chelsea have developed a unique system of managing their squad. They own a lot of players, send them on loan to develop and then either bring them back to the first team or sell for a fee.
As a result, many Blues ply their trade at different clubs on season-long contracts, with Chelsea "renting" them to other sides.
This is perhaps what Liverpool fans meant when they sang the 'rent boy' chant at Gilmour.
Is it homophobic?
Kop Outs!, an organisation for Liverpool's LGBT fans, called out their own fellow supporters for the 'rent boys' jab.
As a Liverpool fan Tim Parkes explained in a post retweeted by Kop Outs!, the chant is homophobic because it uses a term reserved for gays with an intent to offend.
"Respectfully, it is [homophobic]. Rent boy is a pejorative term for a male prostitute who caters specifically for men," Tim Parkes tweeted.
"To use the term in a derogatory manner is homophobic. The origin or supposed 'context' of the chant is irrelevant. It's homophobic.
"Don't sing it, or even defend it."
Chelsea Pride, a Chelsea gay fan group, backed Kop Outs! in a statement.
"We will continue to work with clubs and authorities across the game to ensure homophobia, biphobia and transphobia are kicked out of the game.
"There is no place for hate in football."
