Definitions by Ms. Busa
cos
It means change of subject. It is used more in the mediated communication genres such as texting, pming, iming, emailing, smsing, picture messaging, blogging, and ect...
Lisa Smith: Do these pants make my butt look fat?
John Smith: Hey babe, COS, we are going to be late if we don't leave right now!
John Smith: Hey babe, COS, we are going to be late if we don't leave right now!