Chips and Gravy

Why is it that when you go into a cafe' and ask for chips because you brought your own gravy people give you odd looks, it's not as if i asked for bread i brought my own bacon lettice and tomato, then of couse the mafia are always watching you waiting for you to spill a little bit of gravy at which point they'd wipe their expensive suits in it and say now you'll wake up with a horse head in your bed haha.