Dr Josef Khan reacted after Prof Udo Schukleuk and his partner parked their bikes against his fence while house- hunting in Glasgow's West End. Khan, 43, admitted making the insult - but claimed he was not racist and was referring to Prof Schukleuk's apparent bad attitude.
However, a sheriff yesterday dismissed his claims, and the scientist could now be removed from his 31,000-a-year researcher's job at Glasgow University.
The incident occurred while Prof Schukleuk and his partner Saul Garcia-Lopez were preparing to view a flat on 4 July last year. The men chained their bicycles to a fence on the street in Hyndland, at which point Khan came out "ranting".
Prof Schukleuk, 42, told Glasgow Sheriff Court he repeatedly apologised and tried to retrieve his bike, but Khan blocked him.
It was when Khan eventually went back to his flat that he called Prof Schukleuk "a Nazi".
The professor of ethics at Glasgow University told the court: "I felt it was like something from a racist hate speech. It is not an expression I like and I found it upsetting."
Khan admitted confronting the men as he was fed-up with people parking their bikes against his fence, which he called "an assault on my property" and said he had just spent hundreds of pounds decorating his fence and garden.
Khan told the court: "I spoke to them, but I was measured and polite. However, I felt he [Prof Schukleuk] was being arrogant and that it was as if I was inferior to him."
It was then he claimed he "blurted out" the insult - but only as a reference to the professor's apparent "authoritarianism".
But, Khan added: "As soon as I said it, I thought, 'Oops, that could be misinterpreted'."
Sheriff Johanna Johnston QC said she was not satisfied about his evidence and found him guilty.
Kenny Sinclair, defending, asked for an absolute discharge to be imposed - effectively wiping the conviction from his record - to allow him to continue working abroad.
The sheriff said it was not appropriate and fined Khan 200.