Colleagues of PC Harrison Gray reported the comment to the Met’s Directorate of Professional Standards (DPS) who launched an investigation.
The remark was made while the police officer was off duty at a house party in Bromley on October 14 in 2020.
Bosses quickly placed PC Gray - from the South East Command Unit covering Lewisham, Bromley and Bexley - on restricted duties.
The probe investigated statements provided by other officers and guests who were in attendance at the party.
It was determined that he face a gross misconduct hearing.
A three-day hearing found on Friday that PC Gray had breached the regulations in respect of equality and diversity and discreditable conduct.
PC Gray was dismissed without notice.
Supt Richard McDonagh said: “There is no place for any type of discriminatory language in the Met.
“While I am incredibly disappointed that PC Gray felt it was acceptable to use this language at all, I am immensely proud that his colleagues did the right thing and reported his behaviour.
“They demonstrated what the Met’s values are and that a colleague using such offensive language, even in a social setting, will not be ignored and brushed under the carpet.
“We are working hard to rebuild trust and a part of that process is ensuring that those who let the Met down are rigorously investigated and brought to account.”
PC Gray will now be added to the Barred List so he cannot be employed by police or other connected institutions.