Commentary on Meditations: B9:2

A man of sense and sensitivity would depart the company of men without ever tasting falsehood, pretence of any kind, excess, or pomp. The next best course is at least to sicken of these things before your final breath. Or do you prefer to sit at table with wickedness? Has your experience not yet persuaded you to shun this plague? Because the corruption of the mind is much more a plague than any such contaminating change in the surrounding air we breathe. The latter infects animate creatures in their animate nature: the former infects human beings in their humanity.

In this passage, we really see the contempt Marcus has for "the sins" he described in passage 1 of Book 9.  Rather than endure and potentially be "infected" by the company of pretentious, pompous liars, one should leave.  According to Marcus, protection against such vices is more important than becoming infected by airborne viruses.  All that he is attempting to say is that we become like the company we keep.  If your friends are liars, boasters, seekers of fame and people who are focused on finding happiness in externals (riches, fame, avoidance of pain, pleasures, etc), then you too may become like them.  Better to leave them and seek a life of virtue.

(see also Citadel p. 271)