That is revolting. I don't think I would have been able to keep silent. I can absolutely see myself saying "Excuse you?! That is disgusting!" very, very loudly. I am not (generally) someone who finds humor in such things--unless it's a baby doing it, because pretty much everything babies do is delightful--but this is especially nasty and unfunny. That vile mass of flab is so inhuman, so far from civilized life, that she just deliberately does that in the direction of a total stranger, and doesn't even have the grace to apologize. My theory: she's a coprophiliac, using innocent bystanders like yourself to get her creepy paraphiliac rocks off, just like how autogynephiles get off on forcing other people to play along with their paraphilia. Every time she can do something like that to a man--especially one who is fit and attractive--she feels aroused, and part of the arousal is the knowledge that she did this without your consent and that you are invariably reacting to it.  That's just my theory, though.