Hey, is that my bag?

What is going on in San Francisco?  The past 24 hours have been particularly full of crazy, somewhat scary people.  Last night I was eating at Ryoko's Sushi in the TenderNob.  I was at the bar and there was a guy sitting next to me who had a clear plastic bag wrapped around his left forearm, which had a bunch of tatoos (maybe the plastic was to protect him).  At some point I became aware that he was listening in to my conversation, but it didn't really bother me...until he said "Uh, I'm not eavesdropping or anything, but can you tell me what the last two words you just said were?"

I had absolutely no idea.  I turned around to look at him shrugged, "I don't know."  This perturbed him.  "What do you mean you don't know?  I mean y-y-you just said it and I just want to know what the last two words were."  There was no way I was going to remember what I said now.  "You look like a pretty smart guy, you can't remember what your last two words were?  You just don't want to tell me or something?  Is that it?"  In my calmest most reassuring voice I told him I just didn't remember and that I really wanted to tell him, I just couldn't.  After some pacifying he eventually said "Oh, yah, well, there you go I can't remember what my last two words were either.  Yah, I guess you're right."  He left soon after to my relief.

Then today I got coffee at Blue Bottle on Mint St. and as I was unlocking my bike this muscular but kind of strung out homeless guy rides up and mutters "I think I lost my bag."  Then he's talking to me "Hey, I lost my bag, is that it?" he says pointing at my black Jack Spade bag.  I decide just to ignore him and walk away.  He keeps talking to me though "Hey... hey, I think that my bag.  Hey I'm talking to you!", his voice trailing off as I walk down the street.  Then it his voice gets louder again as he rides up behind me on his bike "Hey, I'm asking a question.  I think that's my bag.  You want to cause a scene?"  He's rolling slowly at walking speed just behind me.  He raises his voice to gain support from the various riff raff around the Mission and 5th bus stop "Hey, Hey, he's got my bag!"  The guy passed out against the federal building continues to be passed out; the guy with a bag full of plastic bags at the bus stop continues to watch for the bus on Mission.  I keep walking.

I start to cross Mission and he's still following "Do you want me to call the police?  Huh?"  I tell him "Its my bag, go ahead."  He follows me a little further, then stops while continuing to shout at me as I walk down Mission.  I turn the corner at 4th St and he's gone.  Why did these people descend on me?