How honest should you be? TO what extent... You're trying to be an honest friend. How honest can you be?
Should you say, "You're an ugly fella, mate... Girls aren't naturally attracted to you as they are attracted to me, so change your approach"
"You're butt ugly, get over it."
"You smell funny today... I don't like it"
"Seriously, your hair 'style' sucks, get a new one..."
"You are fat, lose weight."
"Unless you improve your fashion sense, I will stop being friends with you."
How honest can you be? A good friend is an honest one, as they say...