合わないひと、相性が悪い人って英語でなんて言うの？

"合わないひと"
People who don't click.
People who don't match.
People who are not suitable (得に恋愛）

"相性が悪い人"
People who are not compatible / people who are incompatible.

合わない人に会った
I met a person with whom I just didn't click.
I met a person with whom I just don't match.
I met a person who wasn't really suitable for me (得に恋愛）
I met a person that I'm not really compatible with.

ご質問ありがとうございます。

①　"The person I met was not someone I could get along with."＝「仲良く付き合えない人と出会った。」

②　"I met a person with whom our personalities clashed."＝「お互いの性格が衝突する人と出会った。」

☆　"personality clash"を名詞として使うこともできます：　"We had a personality clash."

ご参考に。