Let's face it. Apart from some who are into scat (NOT me!) it is quite unpleasant when it happens.
But, as a bottom, as much as I do my absolutely best to be as clean as a whistle before I know I am going to receive some introduction, I also know that men don't have pussies, and manholes have a main function which is not exactly getting fucked so, as many douches taken and consuming fiber and blah blah....shit can happen!
If it does happen, as annoying as it is, I think it's up to both participants to the activity to make it light of it.
Unless the bottom is just an "I don't care" kind of guy, a pig, and did not do anything to try to avoid it could happen...