This is a huge question for me. When one of my peers makes some joke about drinking or hooking up or whatever am I supposed to tell them off or just stoicly frown at them?
Or say the Jesus prayer and repent of your own sins.
I think what we do depends on the situation. Is the person likely to listen and consider what you say? Or would it be better to subtly change the subject, neither frowning nor telling him off, but guiding the conversation to a better place, and if that can't be done, to pass over it in silence.
Personally, it makes me cringe when people blaspheme and use the name of our Savior as a swear word, but I've come to realize they're not even aware of what they're saying--that's how bad it is. If people aren't aware, it would seem more difficult to correct them because you need to make them aware, and make them care, and sometimes, if they do change behavior, it is not for the right reason, that is, it's for your sake, which may not be beneficial.