You don't have to use it for a long time. You can talk about Marx and Marxists and Marxist ideas. You don't even have to mention Marx all that much. They'll realise they've become a communist too late.

I was unaware that Marxists were communists. I mean, I knew that communists could be Marxists. But when I heard my friends talking about Marx, it never crossed my mind that they might be communists because that's outrageous. By the time I realised, it didn't matter. Marx was clearly right. Whatever follows from that conclusion, so be it.

The state of political education even among graduates is woeful. You can use the confusion to your advantage; and let your friends come to their own conclusions about their own politics. In the meantime, you can give them an accurate picture of the world to guide them along the right path.