from Battlestar Galactica -- a daggit was an ugly dog-like critter, so it's used as a generic insult, in place of bitch
, especially at school. Extra value, as it rhymes with faggot
Judy: Oh, Brends, you're such a daggit!
Teacher: What did you call her?
Judy: that cute little alien critter from Galactica cuz Brenda's acting silly!