I have so many, but I will say my biggest one on GC is the incorrect use of the apostrophe. For some reason people seem to think acronyms can only be made plural with an apostrophe s.
"There are 2 PNM's in my group." Instead of... "There are 2 PNMs in my group." or, "How many AOII's will be there?" Ugh.
__________________ Adding 's does not make a word, not even an acronym, plural