First of all, according to Wikipedia the Olsa Territory was populated by Poles, Czechs and some Germans -- and Poles were not the majority!
That depends on when the consensus was done. In 1919, the Polish were the majority in the whole entity of the former Duchy of Tscheschen (this not being part of the former Kingdom of Bohemia), and pretty much possibly they were also the majority in the Olsa Territory (Zaolzie, the left bank of the river Olsa). I'm sure that Boletus, if he passes through this thread will be able to provide the statistics, he's very good at finding old ones). Things have changed over time, however, and if in 1945 Poles formed a very significant part of the Zaolzie population (I believe still the majority at that time), their number has been constantly coming dowm until today when they are truly a minority.
People should really learn to laugh at it rather than feel ashamed. Helena Vondrackova and Maryla Rodowicz once performed a song in Sopot singing together the song "Laska nebeska" and both waving a blue stick around. The audience were laughing good-heartedly, and nobody felt ashamed. Until the crash of Poland in 1795, the Masovians were the subject of constant and wide-spread mockery all around the rest of the country because of their dialect whose certain features were judged extremely silly in all other regions (e.g. telling 'ziamia' instead of 'ziemia'), so anti-Slavic language mockery in Poland may not be particularly directed at the Czech language.
I was exploring Cesky Tesin and the surrounding area a few weeks ago. Very, very strange place linguistically...
Why was it so for you then?