他总是趁机占便宜，真是个不可信任的投机分子。

He's always taking advantage of situations—a real ___chancer who can't be trusted.

那个家伙就是个投机分子，专门利用别人的困境为自己谋利。

That guy is a real ___chancer, always taking advantage of others' misfortunes for his own benefit.