あいつはいつも遅刻するんだよ。
That guy is always late.
あいつに任せたら失敗するに決まってる。
If you leave it to him, he'll definitely mess up.
Familiar and somewhat rough way to refer to an object or animal, similar to 'that thing' or 'that one'. Often implies the speaker doesn't hold the referent in high regard.
あいつ、もう動かなくなっちゃった。
That thing stopped working.
あいつはどこに置いたっけ?
Where did I put that thing?
Being late was that guy's fault.
Don't act all high and mighty when you're just that guy.
Next time I see that guy, I'm going to tell him off.