I've had two "on your left" incidents that left me pretty convinced that inexperienced cyclists (and walkers!!) don't know what it means.

Case 1: Country road with center lane marking, couple is out cycling.. they were riding one behind the other on the right side of the road, until the rear cyclist glanced back and saw I was approaching (I was about 100 yards back). Instead of staying where he was, I presume that he moved up along side his partner to let her know I was coming up... however he did NOT move back... they rode two abreast as I approached and didn't make any sign of moving. I shouted out "on your left" when I was about 20 feet back (I was going quite a bit faster than they were, so that should have been just enough time for them to react stupidly and correct) and the guy MOVED LEFT, essentially blocking me from passing without going over the yellow line... WTH?! Now, since there was obviously no oncoming traffic, I did just cross that yellow line and pass on the left.. and I looked back and Mr Stupid had moved over to the right again. I'm not sure what he was trying to do - make me pass inbetween them? (there was enough room, technically, but both he and his partner were somewhat wobbly looking riders, so I felt it better not to take a chance with that one).

Case 2: Hike and bike trail at the park. Path is about 6' wide, paved. Couple is walking hand in hand taking up most of the path.. I slowed down a bit, said "on your left" as I approached, and the man stopped in his tracks, and stayed where he was (left side of the path) the lady also stopped, but turned around, put both arms out (???) essentially blocking the whole path and I ended up off the path and off my bike (not a fall exactly, but no traction in gravel I pretty much skid to a sideways stop and hopped off). She apologized profusely, but it still left me thinking that people just don't have a clue what proper passing entails... it's not like I expected them to hightail it out of my way (just moving over a bit to the right would have given me more than enough room to pass safely), but to STOP and effectively block my way completely? Uh, no....

I certainly know to move to the right when I hear "on your left" and NOT to look back or swerve, or stop, or do anything equally LAME... it's not hard?