few comments
Brake Check, swerve, sign language - these are all things that make the situation worse. Even if your intentions are good, someone who thinks you cut them off will take these gestures as a bad thing.
In this situation, when you first got in front of him, at the earliest convinience, get in the right hand lane. Don't slow down to pace with him, just move over and continue driving. If he paces you on the left, just look straight forward and ignore. People who think you've done them wrong, will forget about it much more quickly if they can't get a reaction from you.
Personally if someone cuts me off, then soon after moves over and lets me pass, it appears to me that they made a mistake cutting me off in the first place (blind spot). If they stare at me, swerve, brake check or otherwise aknowledge a situation, it makes me think they did it on purpose.
One other thing to note: It is a sad day in America when every situation depends on the good guy bowing down to the bad guy. With our current laws, its an unfortunate truth that we have to do this to have the law on our side, but it just hurts the heart knowing our country has gone so far down hill...