Q. How do I make an MLA in-text citation for a comment on a Youtube video?

MLA in-text citations for electronic sources with no page numbers only require the name of the author in the citation.  If you know the author's real name, use it in the in-text citation.  If not, use the screen name of the comment's author.

Examples:
The reaction to the music video was overwhelmingly negative, with its Youtube comments section full of insults such as "This makes me wish I only had four senses" (L33tHaxor91).

Youtube commenter James Bauer said the movie trailer looked like it was shot in someone's garage.