Sometimes making a left turn from the right lane on a bicycle is incredibly difficult and dangerous on a bike. I have to make a left turn off of Fauntleroy on my way home during rush hour, from the right side of the lane. Oftentimes, especially if traffic is fast and aggressive (it varies day to day), I need both hands on my bars to maintain a straight line and cannot signal until the last second and I try my best not to cut in front of cars...sometimes I actually have to pull over and wait for a break in traffic or hit the pedestrian signal. This is with Sharrows though rather than a bike lane, and I am in the same lane as traffic, and thus, traffic should yield to a left turning vehicle.
Bike lanes are more tricky as they should be treated as a travel lane and moving from one travel lane to another requires yielding to overtaking traffic. But there's no real lawful guidance about how exactly it works (which contributes to the confusion I am sure). And if moving into the left lane from the right lane, again, the moving/turning vehicle should yield. On a bike this is a much trickier movement - especially in dense, fast traffic with drivers that already don't want a bike in front of them. Your comment about wanting to get all aggressive to the cyclists pretty much sums it up. Where are you encountering this behavior? Does the bike lane just sort of "end" and cyclists are immediately merging into the street?
Cyclists to use hand signals unless it's too dangerous to let go of the bars:
SMC 11.44.140 Hand signals.
A. All required hand signals shall be given in the following manner:
1. Left turn: left hand and arm extended horizontally beyond the side of the bicycle...Such hand signal shall be given continuously during the last one hundred feet (100') traveled by the bicycle before initiation of a turn, UNLESS during the last one hundred feet (100') both hands are needed to control or operate the bicycle.
Note the above applies to drivers as well:
SMC 11.55.240 Turn signal -- Distance in advance.
A signal of intention to turn or move right or left when required SHALL be given continuously during NOT LESS than the last one hundred (100) feet traveled by the vehicle before turning or moving right or left. (RCW 46.61.305(2))
Drivers to yield to vehicle in front of them:
SMC 11.53.205 Overtaking a pedestrian or bicycle.
The operator of a vehicle approaching a pedestrian or bicycle that is on the roadway or on the right-hand shoulder or bicycle lane of the roadway shall pass to the left at a safe distance to clearly avoid coming into contact with the pedestrian or bicyclist and shall not again drive to the right side of the roadway until safely clear of the overtaken pedestrian or bicyclist. (RCW 46.61.110(2))
SMC 11.53.100 Operate in single lane.
Every vehicle shall be driven as nearly as practicable entirely within a single lane and shall not be moved from such lane until the driver has first ascertained that such movement can be made with safety. (RCW 46.61.140(1))
This is a major contributor to tricky lane changes...drivers driving too close to one another:
SMC 11.53.120 Interval between vehicles.
The driver of a motor vehicle shall not follow another vehicle or bicycle more closely than is reasonable and prudent, having due regard for the speed of such vehicles or bicycles and the traffic upon and the condition of the street or alley. (RCW 46.61.145(1))
So if a cyclist has signaled, and moved into the left lane (or is in the only lane or turn lane signalling left) and is still signalling a left turn off of the roadway, traffic behind the cyclist must yield and not pass on left otherwise drivers are interfering with the operation of "overtaken traffic"
SMC 11.53.210 Limitations on overtaking on the left.
No person shall drive a vehicle to the left side of the center of the roadway in overtaking and passing other traffic proceeding in the same direction...and unless such left side is clearly visible and is free of oncoming traffic for a sufficient distance ahead to permit such overtaking and passing to be completely made WITHOUT INTERFERING WITH THE OPERATION of any traffic approaching from the opposite direction OR ANY TRAFFIC OVERTAKEN.