The head-banger (or "bounce spin," meaning that the skaters try to create the illusion that the girl's head is in danger of being bouced off the ice with every rotation

) is a decades-old staple of Adagio Pairs performances. (In acrobatics, "adagio" refers to a couple posing in stationary balancing positions.) As Anna K mentions above it is not actually dangerous because the girl's shoulder will hit the ice before her head, plus she can protect her head with her arms if something goes awry.
I would venture to guess that it was forbidden in ISU competitions so that a boy learning how to skate would not say to himself: "that looks cool -- I'm gomg to try it with my little sister."
It is heavily featured in small venues like night clubs and cruise ships because you don't need much ice to do it (unlike, you know, actually skating).
I once found myself in a tiny night club in Paris, where the stage was maybe 8 feet by 8 feet. One of the acts was a father-daughter roller skating team. The act consisted of the performers holding two hands facing each other, then spinning around like that until they worked up enough angular velocity to do a headbager or Detroiter or rotational lift.
The Detoiter, in which the woman is held over the man's head paralle to the ice while he spins -- like a well-choreographer preofessional wrestler spinning his victim overhead before executing the body slam -- was named after the
Detroiter airplane (the girl is the propeller), manufactured in the 1930s. It was famous for being the first passenger plane that featured a heated cockpit.