When I asked an FA about this a while ago, he told me that is should be treated like any other passenger making an obscenely loud noise: ask him/her to stop. So, when that FA asked that man to stop, he effectively woke him up and the man apologized. Since it involves other pax, and FA's are trained to deal with this, just notifying them that you don't want to wake them up but want them to stop, and they should take care of the rest.