So I was sitting up at my local Maverik (gas station) with my GSD, Titan, and a guy walks up to me. Keep in mind, I had been there for over an hour waiting for a friend, so ALOT of people had come up and pet my dog. And he was great with them. Kids, teens, elderly, and even a couple buddhist monks that were staying at the hotel across the street, on their way to SLC for a seminar. So this random guy, 50'-60's, walks up to me. I'm a nice person, but I could tell titan was instantly on edge. So i put him on a down-stay, and he behaved just fine, the guy pet him and everything. But as the guy was about to walk away, Titan's fur prickled and he growled and snapped at the guy. Any ideas why? I could clearly tell the guy was a meth addict, myself being a recovering one previously, but that couldn't have set him off, could it?