Good question! Fischer springs to mind for obvious reasons, though I still admire his chess playing immensely. I also have a self-admittedly unfair dislike for Carlsen, simply because he's successful and I generally tend towards the underdog.
It's difficult for me to provide two or more reasons for disliking any chess player, though. I considered stating Botvinnik due to the politics surrounding him, but any criticism should probably be levelled at the Soviet Union and the Soviet chess federation. For one thing, Botvinnik managed to avoid signing the letter condemning Korchnoi after his defection.
I assume that Kirsan Ilyumzhinov plays chesss, and so I'll tentatively go with him for my least favourite chess player, for the following reasons:
- There is a strong possibility that his election as head of FIDE was due to corruption.
- I have questions about how he is running the organisation.
- There are far too many pictures of him associating with horrible people, eg. Muammar Gaddafi & Bashar al-Assad. This is alone should be reason enough to dislike the man.
Two or more reasons.