When a girl (rarely a guy) turns from being a loveable, kind, friendly, and caring person to the exact opposite and transforms into a person with an ugly personality (a bitch). Most cases occur because of influence from others with CMD, other times is due to personal events. PMS and CMD can be easily confused, but CMD is long term. CMD is curable, depending on how sever the case is, it helps to have friends and family be honest with the subject and for the subject to be willing to change their attitude.
X was once friends with Y but X started flirting with the rest of the alphabet including Y's boyfriend Z. The reason for X doing this was because W had been doing it first and X thought she looked just as good as W. X was a victim of Cunt muffins disease (CMD) due to W having CMD first.