A parent who shows up unexpectedly and explodes (like a SCUD missile). This can happen at school, sports, etc. Typically a SCUD parent shows up, throws a fit, and is gone again for another semester.
Jacob's got a major SCUD parent for a mom. I haven't seen her for six months and she shows up here making an ass of herself and just about ripped my head off. Related types of parents: helicopter mom, MIA mom.