A PC is an example of a tar baby. When you punch it, you gets stuck. But here, I'll let Uncle Remus explain it:

"Brer Fox went ter wuk en got 'im some tar, en mix it wid some turkentime, en fix up a contrapshun w'at he call a Tar-Baby, en he tuck dish yer Tar-Baby en he sot 'er in de big road... present'y Brer Rabbit draw back wid his fis', he did, en blip he tuck 'er side er de head. Right dar's whar he broke his merlasses jug. His fis' stuck, en he can't pull loose. De tar hilt 'im.