Gosh, I thought it would be hard to top the one about trading in orphans, but this one is pretty astonishing. (-:
I agree that the entry is wrong, but who knows what it was supposed to mean. As far as I know, 'Um Gottes Willen' does not mean 'shit',' it means 'For heaven's sake,' etc. ('For God's sake' can actually be fairly serious in English, really exasperated or pleading, so it may be something of a false friend.)
This might have been an attempt to translate 'Shoot!', which is a very mild American exclamation, only about like 'Verflixt noch mal,' 'Mist,' etc. I wouldn't even call it slang, just colloquial.
Along the same lines, I'm very partial to a 6-gear exclamation coined by Amy-MiMi: 'Ratten!'