DS is 3 1/2 and still driving us crazy. DD is 6 and has always been pretty easy to deal with, sensitive, kind and no trouble. Bit stroppy and odd tantrums at 3 but nothing unusual.
DS is now the middle child (brother is 18months) so MIL and mine keep saying 'it's because he's a middle child' 
He wasn't great at 2 before his brother came along.
He seriously has a problem following simple instructions....get your socks from your drawer results in him bouncing on his sisters bed, having passed by his own room on the way. Giving him some toilet roll to wipe a runny nose results in the toliet roll thrown around the room and ripped to pieces, while the nose is still running. Punching his sister for no reason, leaping, roaring, poking and hitting the baby. Bouncing around shops, throwing toys around the house for the sake of it. He's started pulling his pants down and flashing people on play dates and thinks it's very amusing. I sound like a broken record 10 times a day, every day every week saying the same things over and over again.
He does not appear angry and when told off, or explained to that his behaviour is unacceptable he smiles. He is not daft but I'm wondering if he is hyperactive or has some attention issues. He never sits still, doesn't stop talkingm makes stupid noises. Short clear instructions are given repeatedly and he just goes off on his own agenda.
We've tried cutting additives from his food, praise and one-to one attention, sticker charts. Over the summer he's got worse and we resorted to putting him in his room to calm down. So he trashed his room in the 5 minutes he was in there. It sounds trivial written down, but it's constant.
I try to keep him very busy and active. Give him creative tasks to do such as lego, painting etc
This summer has been a nightmare and I can't wait for nursery to start so i get a few hours away from him. As much as i love him i feel like running away.....