Hehe - here we go again. That pronunciation has a crop-pie sound though it isn't as definite as some I have heard. Its a bit of a centrist pronunciation but closer to crop than crap. If you go through all the online dictionaries with pronunciations you can listen to you find both crop and crap usages. For example here is a more strict pronunciation. crappie definition | Dictionary.com and here http://www.yourdictionary.com/crappie and here Crappie. They all use the crap not the crop pronunciation which I personally use and think is correct.
My argument is always this. Find one word that has "ap" in it that is pronounced "op" where it is used like crappie with a letter before "ap" like trap, snap, clap, happy, or in pappy. It just doesn't happen. If you find the "op" pronunciation its always spelled "op".
Therefore it is my suggestion, respectfully to Slab and MW dictionary and the others that pronounce it the "op" way, that they are incorrect and it should be pronounced "ap" even if it bears a unfortunate similarity to another word that some feel is offensive, even when most of the people who pronounce it the "op" way can swear like a sailors when they smack their thumb with a hammer or lose a big slab "crap"pie at the side of the boat and don't think twice about it.