[Crazywater]

The problem with German is here that it concatenates words without any indication what the break is :)

Your translation is for BauernFängerEi ("farmer catching egg", which doesn't make too much sense), while this is BauernFängerei ("farmer catching/trapping"). "...erei" is similar to "...ery" in English.

I guess the saying comes from the prejudice that farmers are not the smartest people, and therefore people trying to catch/trap/trick/prey on stupid people are called "farmer/peasant catchers".

[SyneRyder]

Ahh! I thought the farmer was the one doing the catching, not the one being caught. (I'd started dreaming up an idiom about "as easy as catching eggs from a trapped hen".) Thank you!