People that pull U-turns at traffic lights really grind my gears because the traffic turning right (into the lane they are trying to u-turn too) have the right of way and the people pulling the u-turn ALWAYS stop and block traffic from the left turn light.
Do not do a U-turn unless you can do 
it safely. U-turns are not permitted: 
• at an intersection controlled by a traffic 
   control signal (traffic lights) unless 
   permitted by a traffic control device 
• where a sign prohibits U-turns 
In urban areas U-turns are not permitted: 
• on a roadway between intersections 
• at an alley intersection 
• at an intersection where one or more of 
   the roadways is an access to a public or 
   private parking lot which the public can 
   access 
Outside urban areas (rural) U-turns are 
not permitted: 
• on a curve 
• approach to or near the crest of a hill 
   where the driver of another vehicle 
   cannot see you that is approaching 
   within 150 metres from either direction
From Here! 
http://www.transportation.alberta.ca/2000.htm