the string attached to the final tampon that is pulled out to signify the end of her "time of the month" and metaphorically refers to those cool little champagne poppers we all have on new years.
Bob:Man, I've been wanting to bang my girl for the past few days so much.
Joe: Why haven't you?
Bob: It's her "time of the month".
Joe: Ah. So then she hasn't pulled the hooray string yet.
Janet:Hell no I haven't.