The opposite end is not an enjoyable experience either. 

Being showered with criticism is not fun. Sure, things like fitting characters into roleplays, or actually using quotation marks for dialogue are very important. However, things get annoying when somebody harasses you to put that period inside the quotation marks, or how "fjord" is the correct spelling instead of "fiord".

Also, give people time to improve, and space for minor recurring errors. Everyone slips up once in a while.

There's no point correcting people if their mistakes don't affect storytelling or comprehension, and I find that telling someone once is enough; not willing to improve to the RP standard is a choice to not participate.