Well, the worst probably involves being abducted and tortured, but I'd expect that to be only if you were at least suspected of being a particular known person

Well, the worst probably involves being abducted and tortured, but I'd expect that to be only if you were at least suspected of being a particular known person of interest. I think the worst likely case if you're just generally noncooperative is being detained for hours/days then sent back and banned from the US for life.