I'm looking for an idiom that describes something (or someone) that keeps on harming or taking from others, as opposed to giving or benefiting them. Or something along those lines. Any input is greatly appreciated.
A white elephant is a gift that causes the recipient more trouble than it is worth - in a sense, "a gift that keeps on taking".
The phrase refers to a story in which the King of Siam wanted to punish a member of his court in a creative manner. As punishment, he gifted him a rare and highly prized white elephant. Since it was a gift from the king, the courtier had to take good care of the elephant and could not possibly give it away, but the problem is, elephants are very costly to keep. Although it looked like a generous gift, the elephant would financially ruin the courtier. The king's gift was intended to harm the recipient in an ongoing manner, exactly the opposite of a "gift that keeps on giving".
An albatross around one's neck (dictionary.com), from The Rime of the Ancient Mariner, is a common expression, meaning "an annoying burden", "a psychological burden that feels like a curse". It's mentioned in the "In popular culture" section of the Wikipedia article on the poem - see also Albatross (metaphor) on Wikipedia.
Open(ing) a Pandora's box
To cause many troubles and problems
Her parents are understandably afraid of opening a Pandora's box if they buy her a car.
If someone or something opens Pandora's box or opens a Pandora's box, they do something that causes a lot of problems to appear that did not exist or were not known about before.
Open(ing) a can of worms
To create a complicated situation in which doing something to correct a problem leads to many more problems
Our boss is reluctant to change the policy now because she doesn't want to open a can of worms.
The evil eye
A look that someone gives other people that is believed to have the power to injure or harm them Cambridge
A look or stare believed to cause injury or misfortune to others.
The presumed power to cause injury or misfortune to others by magic or supernatural means
Cancer is often used metaphorically to mean anything or (scathingly) anyone that is pernicious:
- an evil or destructive practice or phenomenon that is hard to contain or eradicate
• gambling is a cancer sweeping across the nation
• [he is a cancer on our society] [Washington Blade]