K.L.
My son did the exact same thing. Shortly before his 2nd birthday he suddenly became a different person and it was as if he were possessed by the devil. I am very jealous of these people who say it only lasts a few months because we recently celebrated his 3rd birthday and he still throws some major tantrums. Because his verbal skills are better, now he has also added incessant whining to his repertoire . Maybe that is partly because his baby sister came along a couple months ago and he is regressing.
We have tried the "happiest toddler on the block" method, we have tried ignoring him, we have tried removing him from the situation, we have tried taking away privileges. We've tried it all, but nothing seems to work. I am hoping and assuming that he will eventually grow out of it. I know this doesn't help you, but I thought at least you'd know you're not alone with this.