AITBF if I spit in my dogs mouth while playing?

First time poster of anything but honestly this one kinda blindsided me, last night I was drinking with my roommate’s (my brother, his girlfriend, my girlfriend and her sister) and I was wrestling my dog in the backyard, and in the middle of it all I thought it would be funny if I held my dogs mouth open and spit in there like a llama, and while I thought it was hilarious everyone got really up my ass about it, I figured they were just being lame and like honestly he’s MY dog, I can do what I want, so I did it again. Everyone got real pissy after that and my gf threatened to punch me in the face, which I thought was a real overreaction on her part, and the night kinda fell apart after that. The hangover has gone away and I’m in a better mood and patch up all my relationships and whatnot, but I don’t see how I’m in the wrong here at all. Can any of you help me see how this is such a bad thing?