I also haven't seen Kimi wa petto, but if you like very sweet male leads try Kimi ni Todoke, which is a Japanese movie, if you're into anime it's even better than the movie.
Edit:
Ok just watched a trailer for Ki wa petto, hmmm towards the second half High School King of Savvy has something like that. I guess Seo In Guk has the perfect face for those type of characters.
If you don't mind that type of character being the second male lead maybe try Cunning Single Lady, he isn't as goofy, but definitely really sweet. The male lead has his moments as well especially later on in the drama.
Healer and Empress Ki(historical) have a little bit of that, but I wouldn't watch them just for this though.
