Well, isn’t that a hard cookie to crack!

This is a nice mash up “tough cookie” (a person who is hard to deal with) and “a tough (or hard) nut to crack” (a difficult task to complete).  It was overheard in a discussion about the difficulty of a task, so the speaker was clearly thinking about the latter idiom.  Nuts and cookies are the culprits in this mix up, with a side order of “tough” as the common denominator.   I think this malaphor is very appropriate this time of year (a few weeks after Christmas) when the holiday cookies begin to get stale.   Incidentally, cookies seem to be the subject of a few malaphors.  Type “cookie” in my search feature to see the ones on this website.  A big thanks to Elizabeth for hearing this one and passing it on!