to turn a bookbag inside-out
often used as a prank among high school kids
when you skin some one's bag you take out all the contents inside
turn the bag inside-out
and put the stuff in

usually done near the end of class so that the victim will be so busy skinning his or her bag that he or she will be late to the next class

Short for ultimate bias. Typically used by fangirls and fanboys to describe their favourite celebrity amongst the many that they are fans of.