I have had this happen to me on occasion as well, though I am often so much "in my own world" that other people would not be at fault for assuming that I was not paying attention.
It can be a rather frustrating experience, though, and I am sorry that you were treated in that manner.
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I am not a textbook case of any particular disorder; I am an abstract, poetic portrayal of neurovariance with which much artistic license was taken.