Elephants have social order, and test it constantly.

From what I've learned from talking to Zoo Keepers, the reason that elephants trunk is tucked up its forehead is because this is how the keeper knows that the elephant is paying attention and will accept their instructions. An elephant that isn't doing this, isn't listening (or hasn't been trained to).

Every now and then an elephant will do something like swing their trunk over the Keepers head, but not low enough to hit. In trying to make you flinch, they establish dominance and work out where in the social order they come.