A colloquial pronoun for a person (this guy/this fellow), often used with familiarity or contempt.
こいつ、また遅刻してきたよ。
This guy is late again.
あのこいつ、何を考えているんだ？
What is that guy thinking?
此奴は手ごわい相手だ。
This fellow is a tough opponent.
こやつめ、またやりやがったな。
That rascal did it again.
An informal way to refer to a thing or object (this one/this thing).
この箱、こいつ重いから気をつけて。
This box is heavy, so be careful.
新しいスマホ、こいつのバッテリーが長持ちする。
This new phone's battery lasts a long time.
こいつ、使い方が少し複雑だね。
This thing is a bit complicated to use.
An interjection used to call out to, scold, or express surprise/anger at someone (hey you!/you bastard!).
こいつ、ふざけんなよ！
You bastard, don't mess with me!
おい、こいつ！聞いてるのか？
Hey you! Are you listening?
こいつったら、ほんとに困ったものだ。
Honestly, this one is really a problem.