I was thinking about this while riding and not calling "on your left" and ignoring people making sudden u-turns tonight.
If I was the guy making the U-turn .... I would have to say the fault was 100 percent mine. If I was stupid enough to pull toward the right as i slowed (which is normal for me and probably others) and then suddenly decided to do a U-Turn, and, Without Looking, turned my bike perpendicular to the path of travel, thus likely blocking Both lanes .... yeah, my bad, 100 percent. Definitely I need to Look before I make a maneuver like that. basically, I pilled into the road and blocked traffic without bothering to check if there was traffic. Yeah ... My Fault One Hundred Percent.
If it had been me overtaking I wouldn't have gotten hit, Not because I would have yelled "On your left"---(I might have, but usually don't as it elicits shocked and irrational responses) but because after more than five decades of riding and seeing all the varieties of stupid human tricks, I wouldn't have trusted the guy to not do something stupid.
That doesn't make it my fault, no matter if I yelled or whatever. It is the other guy's Fault.
Of course, legal liability is kind of secondary if you break your bike and body .... and there are both concerns here, personal safety and legal liability.
But yeah .... I don't see how the U-Turner wouldn't be completely Legally liable.