The act of receiving, or giving fellatio whilst the penis is covered in America's finest condiment (mustard).
There I was, minding my own business next to the concession stand and this girl told me she was going to blow my mind. She whipped out the ole French's Classic and gave me the best mustard job I've ever had.
You guys will never believe this. The hot brunette at the party just gave me a mustard job in the back room.