So how are they doing it? There's a chicken cheat and a paper cheat (which makes your player paper thin) and a big noggin cheat (which makes your player's head huge)... I've seen some brits doing this during a game and I didn't know there were built-in cheats. :/

If you look in the dossier where it tells you what you have to do to move up in rank and complete the 50 missions, some of them are the cheats. After you accomplish that specific mission, you will be able to turn on and off the cheat.

press the BACK button while in a game and it will list all the available cheats you have. in multiplayer only the host can activate cheats and they apply to everyone so they really arent cheats, just mods.

What does the chicken mode cheat do? I activate that one all the time and have no idea what it does.

I believe the chicken cheat just makes it so when you throw a grenade or use a grenade launcher, you get this annoying chicken squaking noise. I think the "grenade/chicken" still detonate as a normal grenade would do.

Beware, there are some "glitches" on GR that ppl will take advantage of, ie. the most blatant of which is on the POW map where you can crawl underneath those barricks and then stand up. That allows you to see and shoot as if no building was present but opponents can not shoot you. The only solution is you lay down and shoot those bastards' feet