If you ever wanted to say this to someone, but couldn't, say it here! After a frustrating family visit mine is:
Sister - he behaves that way because you never say no and let him have every last thing he's ever wants. To bring his electric ride-on car to our house because my kids have one each and "he'll kick off if there isn't one here for him" is ridiculous and you can't be surprised that he throws such enormous tantrums aged 6! And don't complain your stuff keeps getting broken when you allow him to play football all round the house (and don't get pissy when I don't let him play it in my fecking conservatory)