Sarcasm would be my answer.
A - Metaphor compares things - this isn't comparing a person to anything. It's more of an observation of a situation.
B - Paradox requires the argument to be sound, yet concludes in senseless. Without further information, we can't assume "you don't have a personality" to be a sound argument, because everyone has a personality.
C - Pun requires some type of word play, which this has none.
D - This is the most likely. We expect everyone to have a personality. Someone making a comment like this sentence is suggesting that the person does not, likely as an attempt at insulting their behavior as bland or boring.
