with all respect, i can't agrre with you on that one, mg! pronouncing '-ing' as '-in' in 'ing-ending' words (e.g. 'doin' instead of 'doing' - technically, a completely different sound in the last syllable) doesn't necessarily speak poorly of you and your education. it happens all the time in quick-paced informal speech.
take a look at this saying '(i'm sittin' here), chillin' like dylan'. (if you pronounce it 'correctly', the rhyme won't work). all in all, it's not a matter of education! if you write it this way, though, you'll stress sb's speaking in an informal way.