boredom could be part of it, but I would say the main thing is that he is responding to the arrival of his sibling and that's what you need to work on. Had much the same thing with my dd1 at about the same age when her sister arrived. Consequences, consistency, lots and lots of reassurance. Taking away privileges works (mostly) with my dd - she is now nearly 4.
I have a 2 year old son, turning 3 in march who's behaviour has changed dramatically. Since the middle of November he seems to be rather naughty when socialising with other children, pushing children, snatching not wanting to share. Nursery has picked up on the sudden change of behaviour and that week when he started I was with my friends children who were playing rough with my son, kicking, pushing, biting and even standing on him! And now I think he has decided this must be how we socialise. He hasn't been mixing with these children since as I have gradually been trying to calm him when interacting.
I have noticed in the nursery room it is very basic for him, even though it is for 2 year olds. They have simple puzzles yet my son knows all his colours, recognises letters and numbers and can manage to do 45 piece jigsaws without looking at the picture. Im starting to get the impression he has a photographic memory not just because of the jigsaws but because of other things he is doing. He can also play a memory card game on the iPad with up to 40 cards very easily. I'm starting to think maybe his behaviour is due to frustration on being bored in nursery room?
I've tried the naughty step but it doesn't work, he gets a row and cries but within a few minutes he will do it again. He is so head strong and no is not in his vocabulary! I've noticed when he is playing sometimes he is actually just hugging very rough and I don't know how to get him to be gentle. I repeat it constantly to be gentle but it doesn't work.
I don't know if this is typical 2 year old boy behaviour or if he is trying to tell me something!! But I'm starting to get scared to go out in public. I should also mention in September he became a big brother so there has been change!