"A man of around 35 years old started shouting: 'Fucking lesbians, they should have sent you to the ovens'!" Paola Concia told Adnkronos.
Concia said that of all the many passers-by on the via Campo Marzio near the Italian parliament, only one woman and a conservative politician, Antonino Lo Presti, came to her and her partner's defence.
Some people even took the 'homophobic' man's side, she said, adding that it was not the first time she had been publicly insulted.
"But this time it was more violently aggressive - I could sense this man's contempt. Why should I accept such insults?" said Concia, who introduced an anti-homophobia bill in the Italian parliament that failed to become law.
Italy's gay rights association Archigay swiftly condemned the incident.
"This is an outrage against the Italian parliament and the battle for equality and justice for gays, lesbians and transsexuals in Italy," the groups said in a statement.
Politicians across the political spectrum also deplored the insults to Concia.
"I express expressed solidarity with the victim of a vile and vulgar intolerance that must be unreservedly condemned," said Italian senate speaker Renato Schifani.