There's a great book that came out years ago called "The Gift of Fear", written by a security expert named Gavin de Becker.
The essential message of the book is to urge people to pay attention to their instincts. People must not allow things like embarrassment and the pressure to be "nice" to override their God-given sense of fear when it's appropriate to be alarmed. If people see something they think might be wrong, they ought not feel stupid (and they ought not be ridiculed) - they need to report it.
After all, if you're dead, how good can you feel about having been PC?