Unattractive, unstylish, or uncool — describes an appearance or behavior that looks awkward or embarrassing.
転んで靴が泥だらけになって格好の悪い姿になった。
He fell and his shoes got covered in mud, making him look awkward.
あの髪型は少し格好の悪い印象を与えるかもしれない。
That hairstyle might give a somewhat unflattering impression.
プレゼンで答えに詰まると格好の悪いから準備しておこう。
You'd look bad if you got stuck in the presentation, so prepare in advance.