That's a nickname that's aimed at their fans, which was in a derogatory way by Aberdeen and Dundee fans, but was accepted by them.
Their official nickname is The Terrors.
edit: just found this from
http://www.dundeeunitedfc.co.uk/index.asp?pg=216
ARABS
The collective noun applicable to supporters of Dundee United. It is now fairly common currency among tabloid sports journalists, though some remain confused as to whom it actually refers, sometimes mistakenly using it to describe the team. Just as Hibees are the team while Hibbies are the fans, Jam Tarts are the team while Jambos are the fans, so Dundee United are the Terrors while their supporters are Arabs (the definite article is rarely used).
The origin of the term is guaranteed to spark debate amongst United fans and there is no definitive answer. It is fair to say that the most commonly accepted version dates back to the mid-1960s. The winter of 1962/63 was particularly harsh and United had already been denied two matches due to Tannadice being icebound. Desperate to play a Scottish Cup tie against Albion Rovers in January 1963, United hired a tar burner of the kind used by road-layers to melt the ice. However the predictable after-effect left the playing surface all but devoid of grass. Undaunted, the directors ordered several lorry-loads of sand, spread it around, painted some lines on it and, astonishingly, the referee pronounced the ‘pitch’ playable! United won the tie handsomely, prompting some observers to comment that they had taken to the new surface ‘like Arabs’.
The supporters, however, quickly hijacked the name for themselves, the next few matches witnessing some fans wearing crude approximations of Arab headgear. The practice never became widespread until the late ’70s and early ’80s when it was seen at cup semi-finals and finals. By the early 1990s even the official club souvenir shops were selling replicas of Arab keffiyehs in tangerine and black.
By that time the term ‘Arabs’ had become more widely used, largely as the result of regular references to it by the popular United fanzine The Final Hurdle (see fanzines), which first appeared in 1988.
