There are lots of crap drivers out there that can't even control one vehicle let alone try to keep traffic flowing.
He may have thought that giving you room on his offside would enable you to pass with ease.
I have had people try to stop me overtaking them by taking a position on the centre-line!
I just wait until I can give them a really wide-berth and accelerate away from them.
I drive through Salisbury on a regular basis and have had 'Two stoppie moments' where cars turning right across the flow of traffic have tried to make me part of their 'Bonnet Furniture' - I must be that good looking!
The first guy that did this to me was hit by a fully snorkelled up Range Rover trying the same manoeuvre two weeks later!
Just remember its a 'what goes around comes around thing'!
By the way I think that I spotted you on Monday or Tuesday of last week driving north on the A36 - was it you?
(I was on my blue & white GSXR) ??
)