Sentence:  If, however, some Facebook friend is just dull or mildly disagreeable, I go back to my guiding principle—openness and inclusiveness—remembering how it felt to  be the kid who always got shunned by schoolmates who would have <WSD>unexisted</WSD> me if they could. 
Meaning of the word marked with <WSD> tags:  To cause (someone or something) to not exist.