There's an enjoyable article in Australia's Sunday magazine about fat acceptance in Australia. Apart from a few minor gripes, it's well worth taking a look at. I find terms like 'fatism' and 'weightism' silly.
Even more importantly defining the absence of shame that is pointless and irrational as pride is something that I usually resist.
I don't object to people insisting they have fat pride, pride in their race/culture/sexuality or whatever. I'm just not particularly enamoured of feeling proud about something for the sake of asserting a lack of shame. I feel neither proud nor ashamed to be fat.
Describing a divergence with your expectations as arrogance, haughtiness or pride is itself vainglorious and solipsistic assuming that you are the authority on how people should feel about themselves and can set the standard by which they should measure themselves, regardless of the merits of your case.
There are many reasons to feel ashamed or proud of yourself at the same time as being a fat person. The mere fact of being fat isn't necessarily one of them.