He's not a bad guy; he's just not good at expressing himself.
He has a good heart; he's just socially clumsy/awkward.
①He's not a bad guy; he's just not good at expressing himself.
He's not a bad guy→彼は悪いヤツじゃないよ
He's just not good at expressing himself→自分を上手く表現できないだけだよ
―OR―
He just doesn't know how to express himself→自分をどう表現して良いかわからないだけだよ
②He has a good heart; he's just socially clumsy/awkward.
He has a good heart→彼は良いヤツだよ
He's just socially clumsy/awkward→ただ人付き合いが苦手なだけだよ
Sociallyは「社会的」という意味で、ClumsyとAwkwardは「不器用な、ぎこちない、下手な」という意味の類義語です。
「人付き合いが上手に出来ない人」のことをsocially clumsy、socially awkwardと表現します。
少しでもお役に立てれば幸いです。