Nenshi actually 51.4% of the vote:(http://www.calgary.ca/election/Pages/results/Unofficial-Results.aspx)

And 51.4% is a dismal showing for an incumbent mayor.  The last time an incumbent mayor lost in Calgary was 1980 and Nenshi's showing (I believe) was the worst performance by an incumbent mayor since then.

And yes Nenshi is arrogant.  He is also divisive.  He is also seemingly incapable of chairing Council meetings, one of the few official duties of a mayor. [He asked Council to look into hiring an outside chair.] 

City Council under his leadership was one of, if not the most, secretive in Canada, with way too many sessions behind closed doors.