Only "say potato" reference I see on Chakoteya is from Datalore.
Several Doctor Who universe episodes where Sontarans are described as potatoes though
"And if ever I'm in need of advice from a psychotic potato dwarf, you'll certainly be the first to know." (The Snowmen -- 11th Doctor)
"He's like a potato. A baked potato. A talking baked potato." (Sontaran Stratagem - 10th Doctor))
"The silliest race in the galaxy, that's what Edgar used to say. Like a huge potato with a ray gun. Quite nasty blighters they were, all the same. " (Eye of the Gorgon - Sarah Jane)