This is a pretty common problem, even in a motor vehicle. Some drivers just can't stand to get behind anyone who is leaving a gap in traffic in front of them, so they HAVE TO get in front of you - it's like a moran law or something. Best you can do is stick to your current line, keep your eyes open for these jerks as you approach the turn and leave yourself plenty of bailout room to turn with them.
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"Let us hope our weapons are never needed --but do not forget what the common people knew when they demanded the Bill of Rights: An armed citizenry is the first defense, the best defense, and the final defense against tyranny. If guns are outlawed, only the government will have guns. Only the police, the secret police, the military, the hired servants of our rulers. Only the government -- and a few outlaws. I intend to be among the outlaws" - Edward Abbey