I was once in a situation like this. It was for my birthday.
A group of about ten friends and I went out to a lovely, expensive Italian restaurant for my birthday. The plan was that everyone would pay for herself, and I expected that. When the bill came I was horrified when one friends (who later turned viciously on me) insisted that I not pay and that everyone else chip in for me. I was so mortified. I protested twice, but she, and she alone, determinedly overrode me and collected the cash. I thanked everyone but we all kind of left in silence.
This was long before eHell and I felt terrible for a long time afterward. I didn't contact everyone to pay them back--which is what I'd do now; oh, eHell no; now I would never allow someone to hijack a dinner again and do that--and I ended up feeling deeply regretful and embarrassed for a long time, even now to some degree.
ETA: Sorry, typo. The "not" has been changed to a now. To answer: I was rather spineless and completely embarrassed. I didn't know how to handle it, and I guess I kind of "slunk off quietly." Cowardice won out over courage, I am sorry to say.