Oh, someone else has probably said it already, but I didn't read oll the responses.
I REALLY do feel for you. My DS is 3.5 yrs and we went through a good 4-5 months when he turned 3 (as in angel while he was 2 and everyone else's kids were throwing tantrums to DEVIL over night). I hated to come home from work - I hated to have days off and I was only happy when I was not with him. My DS too has often been described as "too smart for his own good".
During that 4-5 months we resorted to spanking and he got tossed onto the bed a couple of times (things we thought we'd NEVER do) and yes, we too took away all of his toys. We got through it though and we never feel the need to spank any more (though my scary mommy voice does come out once in a while...).
I think what happens with 3 year olds is that at a certain point, their linguistic development gets ahead of development in other areas.... such as understanding consequence and feeling empathy. It makes for a very frustrating time for parents and caregivers. But all of a sudden we did find that DS was compassionate and that consequences became something real for him. The brain connections were made!
It is so hard (not to mention awful!!!) to go through at the time! Just know that others of us have gone through it too... and that there's a light at the end of the tunnel
. My DS is still challenging.... but things are so much better now. And those things I find challenging might very well be things I appreciate in him as an older child/teenager/adult - just not as a preschooler~!!!