I've read so many really bad SF books (most bought at jumble sales, or charity shops, fortunately; when I buy a book full price and it turns out thus I am miffed) that no particular name floats up to the top of the cess pit.
But wasn't there a book that was so badly written that copies were taken to conventions, and there was a challenge; open the book anywhere, and read it aloud until you couldn't continue for laughing; good, trained straight-men could manage eight or ten paragraphs, nobody could do a chapter.
As far as I can tell, the author wasn't attempting a parody, but seriously trying to write the best he could, fast paced adventure and eroticism, which makes the laughter a little cruel; but isn't it something that gets reprinted because of how bad it is is impressive (Yes, I know Harry Harrison did some deliberate takeoffs – Star smashers of the Galaxy rangers, anyone? – but the idea of not realising just how bad you were managing is difficult to absorb.)