When politeness backfires

I just had the weirdest experience. 

It was about 9:30 and I decided to make a run at the grocery store to pick up the few things on my shopping list.  I walked out the back door of my apartment building, and standing just outside was a man having a cigarette (my building is non-smoking, so smokers have to go outside to light up). 

As I passed by him, I smiled and said "Good morning."  He looked at me and said "What did you say?"

"I said 'Good morning," I replied.  That's when things got unnerving. 

"Are you talking to me?"  I nodded.  "Why'd you say that?  Why?" he responded, sounding angrier and angrier. 

At this point, I decided to just keep walking and ignore him.  It seemed the safest bet at that point as I was a little worried that perhaps this guy was slightly unhinged, and I wasn't sure what he was going to do.

He continued to yell after me, and finally I turned and said "I was just trying to be polite, sir.  I'm sorry."  And I walked a little faster towards the grocery store, looking over my shoulder the whole time.  He just stood there, staring at me.

If I ever see him again, I will be sure to give him a wide berth.