People that park their car in the bike lane. I get that there aren't that many parking spaces in Beijing, but for FUCKS sake, the bike lane exists for the bikers safety and not for you to park your shitty car. There is however a special place in hell for the following people. Sometimes there is a small (maybe 2 feet high) fence to separate the car lane and the bike lane. This is great, as it stops people from parking there. UNLESS some cunt decides to park their car RIGHT in the entrance of that fence, essentially blocking off the entire bike lane(which sometimes is over half a mile long). This then force s all the bikers to drive on the road with the cars. Most of the time that's okay, but just VERY slow.
I guess that's the worst of it. Other that that it's just people seeing the bike lane as a "multi-purpose lane" where everyone can do whatever they want. I've seen quite a few people pushing people in wheelchairs on the bike lane, mostly because the actual sidewalk is designed like crap(ie large holes for trees etc).