not good cory I have a fraction of your problem inasmuch as ds has big fine motor problems, so I know he tends to use fingers rather than fork if he thinks he can get away with it, because it's easier, and also why he doesn't use a knife. But his problems are just with difficult rather than with pain. your poor ds.
I don't really know what to suggest. How about before the next meal (not when food is on table getting cold or being threatening, cos it sounds like all mealtimes are now threatening, poor all of you, not fun) - anyway, how about you sit down and have a calm chat about why you think good table manners are important.
Then agree how you'll move forward. How about, to take the pressure off you all, you choose 1 particular issue, eg chewing with mouth open, or using fingers, and he only has to achieve that in that particular meal.
re importance of manners - I was brought up with rigourously good table manners thanks to Victorian mum. But I spent some time working as Au Pair in France, and our manners aren't the same as theirs and I remember the mother taking me to one side and having a go at me about my manners. Slightly different, as it was a cultural difference, but nevertheless an illustration of how important people view good manners at the table. Do you take him to restaurants?
Poor him tho - my ds is 9 and can't imagine him having on a daily basis to be contemplating what is a reasonable level of pain.