But vinegar is an acid and the stomach is acid, lipoproteins (which are there) take up molecules that have a neutral charge, so if that's right it would... take it? perhaps?
No because THC metabolites never enter the stomach. THC metabolites get released back into the bloodstream (as a result of fat cells burning) and end up in the bladder (as a result of the kidneys filtering the bloodstream).

Drinking vinegar to pass a U/A is an old wives tale. It was the water chased with the vinegar that got people to test negative (the water served to dilute the metab/urine ratio just enough for the urine sample to register below the tests cutoff level). These people would have passed anyway just on the water alone without the nasty vinegar to go with it.