My son is 2 and a half, recently when he comes home from nursery he will hit himself in the head and say "thick thick thick"
I have no idea why he would be doing that unless he has been called it.
My husband and I have never refered to him as thick, neither has an family members and I highly doubt other 2 year olds in his class would do that at this age, so I am concerned it could be a staff member.
It is very out of the blue for him and I hate seeing him call himself that.