well this happens a milli-second after a cough, sneeze or a little fart, it is the watery shity stuff that skids your boxers, sometimes you arnt sure if it has happened and have to check, other times you know for sure. bum gravy
when practicing anal sex, sometime you may notice a thin sludgy brown liquid on your penis. this is known as bum gravy.
i took home this girl the other night, we had normalsex, then decided to try anal. about five minutes later my penis was covered in bum gravy. not a pretty sight!!!