It's irritates mine! <3 I get a terribly inflamed intestinal tract - [But I still take it.. it's oh-so-good for you!]
Actually, it's not as bad as it used to be. It used to swell up to an alarming size, now it just hurts and I get this 'stiff gastrointestinal' feeling - I just chase it with water and I feel much better after 15 minutes or so.
Then again, many people swear by ACV with cinnamon - howzabout trying a small amount..? Allow it to stay under your tongue or a minute or two .. this way you warn your body about what's coming!