I agree that punk covers suck when they're trying to be knowing or funny by sticking swear words in. I prefer it when they're just incompetent or completely warp the original song out of context. Slaughter and the Dogs did one of 'Waiting for the Man' which sounds more like a terracey version of Status Quo, with all the heroin glam sucked out - I'm sure VU fans would hate it, but it's my fave version. Also Skrewdriver's cover of the Stones' "19th Nervous Breakdown" is fantastic, they just squeeze it into the only three chords they can play, speed it up and then terminate the song halfway through, as if the effort's all just too much.
Not really a 'cover', but there was a fucking awful jungle record around 94/95, that sampled Desmond Dekker's "Shantytown", changing '007' to 'oh oh...jung-gle!". Crap.
I suppose William Shatner decimating "Hey Mr Tambourine Man"'s still the ultimate, though, isn't it?