Get a Hershey's bar and have it so it's starting to melt, nice and soft. Walk into the bathroom and smear it all over the walls. When you come out, call up the FA and say she hasn't being doing her job properly, that the lav is a mess, pointing out to her that there is "crap" all over the lav. While she's still looking confused, rub your finger on the "crap" and put a little bit of it in your mouth, while shouting "see, this is SH!T! There's is SH!T all over the lav! Where have you been that you didn't see this?!"