One comment on the typesetting: as much as I generally like all-caps fonts for manga, it unfortunately breaks the "orz" joke at the end, since it's a purely visual joke.
@feha before the commonly known emojis, there were only emoticons. Aka pictures by a few text letters. Smiley faces such as :3 and and something known now owo and uwu exist. orz and I suppose OTL are known to be a letter picture of a person in despair with their head, hands and knees on the ground (facing left).
@jhadred yes, we know that otl is used as an orz (I literally said as much in the first comment). The question was "what does the all-caps version of otl, the acronym OTL, mean", as a tongue-in-cheek way to show that it is all-caps and thus an acronym (which was also literally said in the first comment, second paragraph).