I think it would be great if you could get someone to vomit on his shoes. It would be like vomit icing on the cake.
Funny you should mention that, A few years ago my wife and I were driving from Reno to South Lake Tahoe. She was not feeling well in the extreme, and I was driving a shade fast to get her to our destination sooner rather than later. I was stopped by a gendarme north of Washoe Lake. My fondest hope was that my wife would surrender to her illness and decorate his boots as he approached her window. Alas, she did not oblige.