joffrey seems so fucking stupid, he just keeps making enemies. he's at war with the north, stannis and renly and decides well that's not enough so he puts shit on his mother and the other lannisters and then executes half the children in the city. so now he has to deal with a possible city riot/revolt. also tyrion, do your damn job and keep the douche in line. SLAP HIM /rant
To be honest, the killing of the bastards was Cersei's doing, at least in the books (airs in 9 hours in the UK) and Joffrey is meant to be a stupid entitled brat.