It's a usual think which most fans seam to misunderstand that in any game most neutrals will want the perceived lesser team to win. For example most wanted Fiji to beat England, Japan to beat SA, Argentina to beat NZ and Uruguay to Wales (for the short time they were ahead). And they'll take the proverbial out of the bigger sides fans until it's no longer on the cards especially if incidents happen like McCaw where some fans of NZ cause a stink about the ref before the game has started, usually think McCaw walks on water and they get surprised when quite a few fans somehow find that hilarious.
Ribbing is part of sport between fans as is wanting lesser sides to beat bigger sides. Just be prepared when it happens to you, if England fall apart against Uruguay I'd fully expect every nation to have a good old laugh at us.