DS was a nightmare from about 18m until he started school!
You couldn't take your eyes off him for a minute or he would climb or destroy something.
Looking back, I think he was probably bored. I was new to the area, had no friends and never really went out much, couldn't afford to take him anywhere and didn't have a car.
We spent days endlessly walking.
He is a very bright little boy, and I think he just needed more mental stumulation.
DD is a dream by comparision, she is happy to just go along with whatever you are doing.
Mind you, she definitely has her mothers's temper so i think when she hits the terrible twos, she will hit them hard