Your sincerity has nothing to do with this matter.
Don't use your sincerity as an excuse to your rude way of talking.
You think JH can accept everything fan says as long as they're sincere?
Well, even if he accept it,
that doesn't mean that you can throw any word at his face.
This is not "my" opinion,
this is a general knowlegde.
No one like to be called "fat guy".
Even if you like to be called "fat woman", I wouldn't call you "fat woman",
because I have to keep myself polite.
I understand you have a good intention, you want JH to lose weight because of his health,
but your word is more an insult than an advice.
English is difficult to learn, and because there is something you don't know, so I'm telling you.
It's up to you to accept it or not.
Not like which you have said,
in fact you can say "JH is fat" to me or to other fans, it's okay, because it's not an insult to myself.
But don't say it in front of JH, unless you want to make yourself a sincere but impolite fan.
You can call him "chubby" other than "fat", chubby is a cute word.
But you'd better not repeat that word many times in front of Jeong Hoon,
no people like to hear "You are fat" or " You are chubby" for many times.
Dear Po,
don't call JH a "Fat guy" or even "F" guy, that's a very impolite thing to say.
You're a fan of his, that doesn't mean you can speak to him in a rude way.
Even if you were his grandmother, you couldn't say those words.
You can write whatever you want and how long you want and then send the letter directly to JH's address. However in dclily collection everybody shouldn't write too long.