Probably, it is about poses that are considered sexual. In this case, it is about exposed armpits. See also post #142556. There is a lot of こうですか！？ わかりません！ on japanese internets, but my japanese skills are not enough to read what it's about.
Well, first google hit looks plausibly like a source, or at least close: http://yet.s61.xrea.com/mt/archives/000108.html T/L: Poster asks to be taught how to ASCII-art of a specific 2ch character, after which someone responds with "Here, I give you parts, figure out the rest yourself", and OP responds with "Like that? I don't understand! Please explain".
