I think it's fair to say "once every month or so" haha... I guess it would depend on everyones opinion, is a one picture post with a paragraph of quality text considered bad? Or is a great video with no text considered bad? I think it's different for everyone, unless your a regular bad poster...But I understand he "give yourself a break" kinda cool and understandable.
I think that standard is set by your previous posts, you know? If you write 5k word posts and then one day you write a 100 word post, then that may be considered a shitpost by YOUR standars, whereas someone who always posts 100 word posts, that one post will just be average. The key is, to what standard do you have you audience used to?