My own kiddo, at the age of two or three, decided that -o was a productive suffix and started calling me and her mother "Daddo" and "Mommo".

I don't think that's actually a diminutive (meaning shifts to add smallness or endearment), just a colloquializer (meaning doesn't change, just becomes less formal; dialects may adopt a particular informal word as standard).

not sure psycho counts, as it works in every language that uses the greek? latin? base.

Also I kinda liked learning about smoko, even as a non-smoker.