Purely guessing here, you might want to avoid tweeting "Stupid fucking white man" at conference organisers. https://twitter.com/0ndras/status/960901913624576001 -- but this is just a guess. I have no idea if that's why they blocked you.
What he writes in the tweets above really comes across as white supremacy-ish and a bit racist - basically blaming the conference organizers that not being accepted is because he is white, or more specifically, is not "racially diverse enough", which imho is just another form of racism... I wound't find the bottom "Stupid fucking white man" tweet (i.e. quote from a great movie) as offending as what he is implying in the tweets above.
Did that second tweet get removed? Can’t see the swearing.
Agreed with the language. It’s a constant stream of fussy complaints, and as unfair as it sounds, I would have probably blocked them too after years of the same.
Then someone @-mentioned the conference, and he replied this in Czech (translation courtesy of Google Translate):
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About three hours ago, they came back from my mail, where they again rejected my talk proposal (or all the Xs that I sent - as every year). Chance? I do not think. :P
Original:
Cca tři hodiny nazpět mi od nich přišel mail, kde opět zamítli muj talk proposal (resp. všech X, co jsem -- jako každoročně -- poslal). Náhoda? Nemyslím si. :P
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In other words, he suggested that his talks were rejected because of positive discrimination towards minority groups, and he's critical of such discrimination.
I understand the conference could take offense with such statements (whether or not the talks were rejected for that reason).