A blanket party is a means of hazing conducted by a peer group. Blanket parties are most frequently conducted by groups within the military or police.
In a blanket party, the victim is restrained by having a blanket flung over him and held down at the corners. Then the remaining members of the group strike him repeatedly with batons, sticks, or any other improvised "flails" (a sock or bath towel containing something solid, either a bar of soap or a padlock).
Officers Jackson, Carlson, and others gave Julien his own "blanket party" as revenge after they ended up losing their jobs as a result of bullying Julien about his homosexuality.