Many people seem to pronounce words like “something” as “somethin” or “he was running through the park” as “he was runnin through the park.” Why don’t people say “this is borin” instead of “this is boring”?
EDIT: I think I have heard people say “this is borin’ me to death” but never just “this is borin.’”
The operant factor isn’t the word, it’s the position of the word in the sentence. It’s much less usual for someone to drop the g from -ing in the last word of a sentence. The two exceptions I can think of off the top of my head are somethin’ and nothin’.
It is not uncommon for boring to be pronounced that way here in the South. We drop pretty much all of our g’s but so does everyone else in the rest of the country if you think about it. It is the vowel in “ing” that changes when you “drop your ‘g’”. It goes from an “een” sound to an “in” or “un” sound. I don’t think anyone pronounces a hard “g” at the end of the word unless the “ing” isn’t an add on. “Ring” would be an example in that case. In most other cases the “g” sound seems to be missing altogether or is so faint as to be inaudible in normal conversation.
Could be somethin’ to do with tongue position - in -thin, the tip of the tongue is going from contact with the teeth (voicless dental fricative “th”) a short distance to the alveolar ridge just behind the teeth (alveolar nasal “n”). This is probably easier than going all the way to the back of the mouth for the velar nasal “ng” as in -thing. But in boring, the tongue starts further back so it’s probably just as easy to enunciate the “ng”.
I don’t think this is it; I can think of lots of cases where sentence-final /ŋ/ is realized as /n/:
What’s happenin’?
How ya doin’?
What’s she makin’?
Hush; he’s sleepin’.
Whatcha cookin’?
I’m laughin’!
In fact, I can’t think of any sentence-final present participle (whether used as a verb, a gerund, etc.) where it’s not permissible to make this sound shift in my dialect, except “boring” used as an adjective.
Because bor-in said in the same manner sounds like another word: born. It takes too long to get out of the R, so the I comes out sounding like a continuation of the R.
How about That’s interesting? I think this situation with boring, interesting, ect., is, in fact, grammatical, in the same way going to is realized as “gonna” only when it grammatically serves as a periphrastic modal. No one says, “I’m gonna the beach tomorrow, wanna come?”
I thought another -ing adjective might have the same characteristics, too. But, while it’s less common, the G is still dropped more frequently with other adjectives than with boring. That’s why I came up with the idea that possible confusion with born might be the problem.