Deliberate mistake: Throughout the entire movie, every time Charlie Sheen is not wearing his helmet, especially when he's out in the field in this tropical climate, his hair is always meticulously combed back, blow-dried and puffy. As a veteran, I know from personal experience that when you take your helmet off, especially in a climate like that, the reality is your hair will be messy, sweaty, pressed flat and most unattractive.
Deliberate mistake: While recon platoon is marching in their modified pt uniform, Gunny has "Cojones" call a cadence. Meanwhile Sgt. Webster maintains control of his formation, but from the wrong side. No platoon leader ever marches their unit from the right side of the formation.