Be not deceived: evil communications corrupt good manners. (KJV)
Do not be deceived: “Bad company ruins good morals.” (ESV)
μὴ πλανᾶσθε· Φθείρουσιν ἤθη χρησθ' ὁμιλίαι κακαί (Stephanus 1550)
Nolite seduci: corrumpunt mores bonos colloquia mala. (Clementine Vulgate)
Be not seduced: Evil communications corrupt good manners. (Douay-Rheims)
Be not deceived. Evil communications corrupt good manners As nothing is easier than to glide into profane speculation, under the pretext of inquiring, he meets this danger, by warning them that evil communications have more effect than we might suppose, in polluting our minds and corrupting our morals. To show this, he makes use of a quotation from the poet Menander, as we are at liberty to borrow from every quarter everything that has come forth from God. And as all truth is from God, there is no doubt that the Lord has put into the mouth of the wicked themselves, whatever contains true and salutary doctrine. I prefer, however, that, for the handling of this subject, recourse should be had to Basil's Oration to the Young. Paul, then, being aware that this proverb was in common use among the Greeks, chose rather to make use of it, that it might make its way into their minds more readily, than to express the same thing in his own words. For they would more readily receive what they had been accustomed to -- as we have experience of in proverbs with which we are familiar.
Now it is a sentiment that is particularly worthy of attention, for Satan, when he cannot make a direct assault upon us, deludes us under this pretext, that there is nothing wrong in our raising any kind of disputation with a view to the investigation of truth. Here, therefore, Paul in opposition to this, warns us that we must guard against evil communications, as we would against the most deadly poison, because, insinuating themselves secretly into our minds, they straightway corrupt our whole life. Let us, then, take notice, that nothing is more pestilential than corrupt doctrine and profane disputations, which draw us off, even in the smallest degree, from a right and simple faith; for it is not without good reason that Paul exhorts us not to be deceived.
John Calvin, Commentary on 1 Corinthians 15:33