"Most biggest"

^ I understand when people say 'never never' or 'very very', but to me 'most biggest' doesn't give the idea of something bigger than 'biggest' - in fact it sometimes does the opposite and just sounds clunky and grammatically incorrect. I don't CARE that much, just thought I'd point that out.

A couple of points:

"Most biggest" or "most fastest" sound like something a foreign speaker would say. Native speakers occasionally screw up and say these kinds of things, but in my experience, they always realize the mistake and correct themselves. They don't consider it correct speech.

An exception may be in african-american slang. I recall a movie awhile back titled "Mo' Better Blues". I think it was directed by Spike Lee. I'm not sure if anyone actually says "mo' better" or whether that was intentionally exaggerated.

I do hear native speakers make this mistake with more abstract words where the good-better-best type of continuum is not as obvious. i'm thinking of things along the lines of "I had the most perfect date last night". Perfect is already superlative. How can anything be more or most perfect?

The fact is I hear it a lot among native speakers here, albeit those whose speech is more colloqual. When you're used to hearing something sometimes you forget about it.