No offence, but... you also thought it was ok to term working-class people as 'common'. Both are definitely NOT alright. 
I really do take offense at that. This is a thread about words having multiple interpretations. I have rarely come across the British version of the word "common" and have formed my understanding of its meaning (until this thread) entirely from the reactions and comments of my co-workers. I think it's unfair to judge my views on class based on my misunderstanding of the British version of a word that I've rarely come across and am still learning the meaning of.
I also think it's unfair to assume my comment on not knowing the word "spaz" was offensive was either "NOT alright" or an indication of my thoughts on disability when the majority of the Americans who posted in this thread also admitted to not ever knowing the word was offensive. I clearly expressed that I was both glad I hadn't accidentally offended someone by using the term in its American context, and also that I was removing the word entirely from my speaking vocabulary.
I really preferred your first response of correcting my interpretation of a British word rather than your second response of using it as fuel to subsequently disregard my future posts and opinions on an entirely different topic.
I'm sorry if I have caused anyone offense by using the term "working class" but am ultimately thankful to Genau's first post and Tremula's as well, which both corrected the shaky British definition I had formed. Clarifying that the British word "common" specifically refers to "white trash" and "chavs" is certainly useful to me and will hopefully be useful to others as well.