The man at the other end of the argument, Azem Hajdari, is one of the biggest bruisers in Albanian politics. A close associate of the former president and present opposition leader, Sali Berisha, he spent most of the recent general election campaign orchestrating a gang of loyal thugs in attacks on opponents.
Early in the week, the burly Mr Hajdari had thwacked Mr Mazreku a couple of times in the parliament chamber as the Socialist Party bulldozed a new VAT law on to the statute books. On Thursday morning the attack appeared to have been forgotten as the two were seen sharing a coffee in the parliament building cafe.
But a few moments later, as they were re-entering the chamber, Mr Mazreku pulled out a gun and fired at Mr Hajdari's chest and legs. Four bullets hit their target. Mr Hajdari is now recovering in a Tirana hospital.
There was more to the attack than politics. Both men come from Albania's remote north, where a medieval honour code operates, and scores are still settled by blood feud.
According to the so-called Kanun of Lek, a series of feudal rules and regulations set down in the 15th century, a physical attack such as Mr Hajdari's merits revenge by death. Albanian press reports claim Mr Mazreku was visited by five or six of his relatives and pressured into killing Mr Hajdari - on pain of being killed himself if he refused.
Mr Mazreku's attempt to comply not only failed to kill Mr Hajdari, it also unleashed the kind of political storm that led to the near-dismemberment of the country earlier thisyear. Mr Berisha and his supporters accused the government of a premeditated attack and called for the resignation of the Prime Minister, Fatos Nano, and his gang of "murderers".
The following night a bomb shattered the Socialist Party's headquarters in the northern city of Shkoder. A shaken Mr Nano appealed for calm on television. As for Mr Mazreku, he now faces trial for attempted murder.Reuse content