Cain't be 7, that was meant to invoke images of Sasquatch.

Probably isn't anything Scottish or Gaelic either, because that's too obvious (and too popular). Therefore I'll cast my vote for 2, right here in this here qualtagh box...

(PS. Are you sure we aren't all being led astray, and it's really the Klingon word meaning "You are such a gullible k'tach!" ?)