<Only applicable if the text "
first post" (Or
similar spellings) is actually in the first post of any given forum, topic, video comments section etc.>
"
First post" is most often used to describe ones "ownage" over all other posters that plan on making a comment.
I.E. "I was here first" "I am better than you" etc.
Its childish to most but to those who would hopefully be "
First poster", seeing your "first post" stolen can mean a tragic loss emotionally, often accompanied by feelings of hopelessness, failure, despair and in extreme cases, suicide.