pronoun
Derogatory or very familiar third-person pronoun for a person the speaker looks down on or is close to. Rough and masculine-leaning; not used in polite contexts.
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.
pronoun
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?