Dissapearing without warning, or suddenly appearing in between two traffic lanes. Take St Kilda Rd and especially the Junction going North as an example. You just never know what action will happen next. Suicide Alley could be made into an amazing puter game. The next level of this umputer game should be set on Swanston Walk, between parked buses and moving trams.
Wayward jaywalkers are another obstacle.
Of course the most frustrating aspect of this level would be the constant stream of red lights. The influx of broken glass and car bits swept into bike lanes but not immediately cleaned. Again where motorists forget that not ALL people travel around in steel cubes. OR When a lazy inconsiderate cyclist fails to pedal at the minimum required speed of 60 kph, and is rightfully disposed of by the righteous motorist who was being fractionally delayed in their life critical mission to make it to the next red light.