Grammar Fan
Fan of grammar. It's their name so capitalize it. That's their not there. I would start it with "and" ,but that's incorrect. That I needs to be capitalized by the way. Btw is incorrect.
You: lol look at that grammar fan.
Grammar Fan: Laugh out loud. Look at that grammar fan! (That's exclamative.)
Grammar Fan: Laugh out loud. Look at that grammar fan! (That's exclamative.)