Dean didn't seemed remotely surprised by the question, he knew he wasn't fooling anybody. "If you bite me? Probably. If you drain me at all ill probably pass out in your car and drool on your nice leather seats.". Back in the day he would have said he'd be fine even if he knew he wouldn't be...especially if he knew he wouldn't be but he guessed being here changed him a little. Why lie if it would only lead to falling asleep in the elevator.