Grammar police.... Grammar police..... Most funnest?......
Old fuddy duddy.
In formal writing,
fun isn't even an adjective, it's a noun, so therefore ergo thus
funner and
funnest doesn't exit. However, in informal writing and speech, it can be and often is used an as adjective. I sincerely hope my reply above isn't considered to be formal writing, as it was meant to be very informal. In any case, the
Oxford English Dictionary recommends
funnest "should only be used in very informal contexts" and
Dictionary.com defines it as the
informal adjective, related to fun, especially social fun,
a fun thing to do; really a fun person; the funnest game. And
The Grammar Girl describes why you're an old fuddy duddy,
If Steve Jobs can call the new iPod the "most funnest" iPod since, like,
ever...