Well, i guess the question comes down to whether or not you feel like human interaction is designed to increase understanding, or to serve you and your personal needs.
If I pull someone aside and say "hey, they joke you made is not okay for x reason", then I'm not furthering the idea that these jokes are okay. And that's the situation that both I, and the person you were originally replying to, are describing as an alternative to getting mad and making a scene about it. Even calmly bringing it up at the time, in front of others, is fine as long as you are not demonizing, or talking down to the person. Just make it clear that it's not cool.
^ you know, KB summarized this much better than I did, so just read his comment in the stead of this section.
the onus is not on me to be able to discern between that and malice
I would argue that, as a human being interacting with other human beings, that that IS your job - to discern meaning in conversation. The point of language is to be understood, and the point of conversation is to ensure proper understanding between others as we share ideas and experiences. To argue that it is not your "job", or that the "onus is not on you" is just shifting the blame. That's like a carpentry teacher saying "well it's not MY problem that you don't understand how to build cabinets". No, the onus is on both people, at an academic level. The teacher must do all they can to be understood, and the student must be willing to work with the teacher until they understand.
Does this occur as often as it should? no, because some teachers don't care enough, some students don't care enough, and sometimes neither have the time because of standardized testing. However, you are emotionally invested, and you have the ability to MAKE time. if a student is willing, then there's nothing you can't teach them - and most students are willing.