Plagiarism is maybe best thought of as an ethical violation. There are a whole lot of contexts to it. There is a difference between plagiarism and copyright violation.

I am not a lawyer but plagiarism, in many circumstances, (depends on location! so beware) is not a crime.

Can someone be sued for plagiarism. Sure, it might be possible. If you're taking someone else's ideas and passing it off as your own, then it probably increases the chances. So it might be wise to attribute it - at least that is transparent.

Saying that, there are instances of uses such as obvious satire or parody that are probably not going to be actionable.

In terms of music, lots of things have to be in context. It is hard to claim copyright on simple and obvious things (simple chord progressions, a few notes in a bar or two of music, short phrases in the lyrics etc). People have tried, but it is a hard and expensive case to win.