"Crummy" Natural Recordings by Native Speakers
The word "crummy" is an informal adjective that means of poor quality, inferior, or unpleasant. It can be used to describe something that is not very good or that has a negative connotation. For example: "The crummy weather ruined our picnic plans."
To crumble means to break or fall apart quickly and easily into small pieces, often because it is fragile, weak, or old. For example, a cookie can crumble if it is dropped, or a person's nervousness can crumble their confidence if they're put on the spot. In social situations, it can also mean to collapse or lose one's composure under pressure.
(The word "crumbly" is an adjective that means having a texture that breaks easily into small pieces, like dry bread or a crumbling cliff. It can also be used to describe something that is weak or fragile.)