The agony and the 'ex'tasy - S4-E1
Plot hole: In the closing scene in Big's car, he asks Carrie how her birthday was, then says, "So how old are you?" She replies, "How old are you?" And they coyly don't reveal their "age box." But they have known each other for 3 years/seasons at this point - dated on/off for 2 years, had an affair, and are just friends now. There is no way they wouldn't know each other's ages. This exchange only existed to benefit the plot of this episode - it makes no sense given how long they've known each other.
Answer: A popular brand of sexual lubricant. See http://www.k-y.com/index.jsp.
J I Cohen