Our DS (4 years old) has frequent tantrums at bed time. This usually happens after the wind-down (brushing teeth, putting on pajamas, reading stories). He will suddenly turn into a monster as though he has flipped a switch from being sleepy cuddly perfect child to screaming or shouting, bouncing nutcase.
He has a younger sister (1 year old) who gets a lot of the attention previously reserved solely for him but it doesn't explain the madness which usually resorts in either me or my DW storming out of his room shouting 'your turn!'.