I had been dating a guy for a few weeks when he called me at work. I picked up the phone and said, "hello" only to hear pig snorting noises on the other side. I didn't know who it was, and so I hung up the phone. He called right back and admitted it was him, but never gave any explanation as to why he was snorting.
I should have known something was weird with this guy right then, but I kind of ignored it. But the animal noise thing continued. He started leaving messages with just barking or meowing on them. No explanation. I only called him back if he left me a real voice message, since I didn't want to encourage this odd behavior. But it continued.
Then he started doing it in person too. I realized that any time I brought up any subject which made him uncomfortable he'd "change the subject" by imitating some animal. But in general he was a good guy, and I enjoyed his company, so I tried to ignore this weird trait which he seemed to think I'd find endearing.
This culminated about two months into the relationship when I asked him if he'd like for us to be dating exclusively.
"Moo!" He said. "Moo! Moo!"
"I guess not." I said.
And that was the end of that relationship.