An acutal Marine's perspective on this movie...
Alright, I only watched the trailer (because there's no way I'm wasting my time with this *beep* but let me tell you right off the bat why a two minute preview of this movie alone has made it the laughing stock of the military community:
1) I've never actually used the term "Jarhead" to refer to myself or another Marine, and no, Jarhead is not a coveted title you earn. The title of Marine is what you pride yourself in.
2) Only non-infantry personnel Marines are still issued the M16 A4 service rifle (grunts are issued the M4); so somebody talking about all their hardcore war-dog training with and M16 A4 will be viewed either as an inaccuracy or a total joke.
3) Probably the biggest of all, the main characters are mentioned to be "supply Marines". To be fair, the bulk of the Marine Corps is non-infantry personnel, and they still are trained in basic infantry and war fighting fundamentals, but the reality is most of them will never see any action or put those skills to use. Which is why it's such a joke that they send five guys from supply on this top-secret mission (not recon, rangers or any kind of special ops unit), and that they fight their way back to Camp Leatherneck with all their mad skills. If you've spent your entire time in the military working in the administrative and logistical side, then no, you're not going to be slaying the entire Taliban by yourself.
4) The part where they're partying aboard Leatherneck and clanking beer bottles with their commanding officer...yeah, I don't even know what to say about that.
5) The phrases "semper fi" and "oorah" are the last things you would be shouting at each other during or after a firefight.