i-adjective
contrived; false-sounding; unconvincing
Colloquial adjective describing something that seems like a lie or feels fabricated; often used for stories, excuses, or performances that lack authenticity.
彼の言い訳はどうも嘘っぽい。
His excuse sounds really contrived.
あの映画の演技は嘘っぽくて、感情移入できなかった
The acting in that movie was so unconvincing that I couldn't get into it.
嘘 is a noun meaning 'lie' or 'falsehood', while 嘘っぽい is an adjective describing something that seems like a lie or is unconvincing.
怪しい means 'suspicious' or 'dubious' in a broader sense, often implying potential danger or deceit, whereas 嘘っぽい specifically focuses on the lack of credibility or artificiality of a statement or performance.
Formed from the noun 嘘 (uso, 'lie') + the suffix っぽい (-ppoi, '-ish, -like'), which attaches to nouns to form i-adjectives meaning 'seeming like' or 'tending to'.