Yes I know, the answer may well be that he's a 4YO. But this is quite recent - he was relatively laid-back until about four months ago (he's now 4.6); had his moments as a 'terrible two' (and three), but always been much easier and more 'reasonable' (as much as a small person can be) than our DD, who is 8 and has always been very full on.
He's generally incredibly grumpy when he wakes up (don't think he can be tired, he sleeps from about 8pm to 7am and almost never wakes in the night, eats well, is active and healthy etc.), and at regular intervals during the day shouts/cries/hits/winds his sister up, says no to dozens of things, often makes a huge fuss about mealtimes saying he doesn't want to eat or he doesn't like what I'm/DH is cooking (in the end he almost always eats it all, just after loads of fuss), loses his rag over all sorts of things big and small, shouts 'You're stupid' and 'Shut up' (things no one else says here, not even DD when she's cross) and whacks us/ throws things... I could go on. Point is, I don't know WHY - maybe it's just a phase, but it seems such a long one, and because he never used to be like this (famous last words) I'm starting to wonder whether anything is actually wrong...
Phew. Thanks for reading this far, if you've managed it. Any advice/thoughts gratefully received!