Mr. Akashi and Mr. Iwamoto
These two teachers are basically Yusuke's nemeses at school. They've got it out for him and his whole friend group, constantly scheming to get them expelled using whatever means necessary.
During the Four Beasts arc, Iwamoto gets possessed by a parasitic makai insect. Under Suzaku's control, he becomes obsessed with killing Keiko and stalks her around campus until Yusuke destroys the whistle controlling the bug. Once the insect dies, Iwamoto snaps back to normal.
Iwamoto also holds the distinction of being the unwitting test subject for Yusuke's first real demonstration of his Spirit Gun powers—getting blasted in the back of the head and knocked out cold. Probably not his favorite memory.
Content compiled by AnimeList.moe from publicly available sources.
