Right. Where I'm from, lack of punctuation and capitalization indicates less serious discussion, irony, sarcasm, etc. A non-serious "mood". If someone starts using correct grammar (e.g. I instead of i, periods, commas for introductory phrases and splices) it's an indication of the serious "mood" and to start a more thoughtful discussion.

It's probably a good idea to tell people this instead of just assuming everyone knows... but it's kind of engrained in the culture of the communities I'm in.