My girlfriend and I adopted a rescue dog like 4-5 months ago, we don't know the breed for sure, but we think he is a Treeing Walker Coonhound based on his looks. The vet thinks he's around 5 to 7 years old and told us that he looked like he had a rough go at it, as he was malnourished, a bit mangy and has a couple small scars/bald spots, but he has been as sweet as he could be since we've had him.
We play together a lot, rough house, I made weird sounds at him, and he always loves it. Last night, we were playing and I was scratching his belly, and then I did a little raspberry type thing (like when you vibrate your lips on a baby's stomach or something like that, I hadn't heard that term before my girlfriend said it), but didn't blow hard or anything, just made a weird sound and vibrated my lips. He aggressively snapped at me when I did that, and I backed away. When I re-approached, he started growling very aggressively. The hair on his back was standing straight-up, and he was just petrified of me after that - hair was straight up and he was shaking for hours.
He is fine with my girlfriend, but so uncomfortable with me. He has taken treats out of my hand, but goes back to being very aggressive and growling after that just towards me. My girlfriend and I walked him this morning, and if I was ahead of him, he wouldn't follow me.
I've been trying to act normal today, and to kind of ignore him - not in a mean way, just a "going about my day" type of thing, and not petting him or getting super close. He still is just staring me down with this piercing suspicion. Anyone has any suggestions/thoughts? He has always slept in our bed, and did so last night, but stayed on my girlfriend's side, and I had a pillow between me and him so I wouldn't accidentally jostle him with my foot or anything.
Any thoughts? I was considering going to a behavior specialist or something like that? But I'd be curious if anyone has some thoughts or has gone through a similar experience with a dog. Will he hate me forever? He does seem a bit better today - in other words, hair isn't standing up and I'm in the same room with him without getting growls, but he still does NOT enjoy my presence.