muqran in Maltese means someone whose parter is cheating on him. An insult implying that the person is being cheated upon. Usually applied during heated arguments in the middle of the road, after one's garage exit is blocked by the opponent's car.
In Italian there is a saying "con le Corne" - with the horns, which is slang for being cheated upon.
Horns in maltese are "Qrun"
Thus the word muqran is derived from "qrun" and refers to a (male) person. If referreing to a female person the term "muqrana" is used.
San Pubulju il-Muqran (Saint Publius the Horned)
Aw ja muqran - ("hey you muqran")
Note: This entertaining insult is mainly directed towards people living in Furjana since their patron saint is Saint Publius. People from Valletta are especially prone to using this insult, especially after Valletta FC win against Floriana FC (since they happen to be arch-enemies).