Learn English – n idiom to describe something that is given under the pretenses of kindness (e.g., as a gift), but which is actually not good?

idiom-requestsmetaphors

For example, when you get those weird chewy caramel things on Halloween; given out of kindness but really no good. I'm thinking of something that is a "false gift", almost like the inverse of a blessing in disguise (which this thread discusses, but none of those are what I'm thinking of).

The intentionality of the giver is not so important as the properties of the thing itself: it is supposed to be good, but really isn't.

Best Answer

A quick answer that comes to mind is "White Elephant".

See Wikipedia White Elephant

A white elephant is a possession which its owner cannot dispose of and whose cost, particularly that of maintenance, is out of proportion to its usefulness. In modern usage, it is an object, building project, scheme, business venture, facility, etc., considered expensive but without use or value.1

There is also a party game in which people set out to intentionally give each other white elephant gifts.

One might also consider

Poisoned Chalice

as suggested here, or from that same page:

A curse in disguise

It's not standard or a set phrase, but it should be easily understood.