[Not a joke] I'm looking for a joke with the punch line 'cha potatoes'

[Not a joke] I'm looking for a joke with the punch line 'cha potatoes'

My mom heard a joke years ago from a coworker with the punch line 'cha potatoes'. Basically meaning 'duh'. She used to say it to me growing up and I thought it was a thing people say but my husband informed me it's most definitely not. I told my mom this and she told me it's from an old joke about a sack of potatoes,but she can't remember the whole joke. Does anyone know this joke?