And if it was directed to me... Jack is going off the assumption that it's Dean, because he has a reason to loathe Dean, and assume the worst. It also ties in with the fact that Jack was aware they were being watched by him. So basically, in Jack's mind, he assumes it's either Dean or some as-yet-unknown-individual(s). He's betting that it's Dean. If he comes across as too confident in that fact, it's because he is a confident person. But rest assured, I'm not metagaming.<br/><br/>