Platoon is rated "R," and with good reason. The biggest shocker in this film is the violence. A lot of people die in this film (some meet their end in a very disturbing fashion, such as the Vietnamese woman Barnes kills and Manny who is tortured and tied to a tree).
Alongside the graphic violence is the language. While Platoon isn't as bad as some newer movies, the guys in this film drop plenty of F-bombs, and repeatedly refer to their Vietnamese enemies in less than flattering terms.