A Shadow Sensei is a Person who master the Shadow Fuck. While shadow fucking you have "sex" with another Person without penetration. After that you can call yourself half a virgin.
Shadow Sensei: yo dudes! yesterday i had some really good shadow sex!
friend: what even is that you weirdo?
Shadow Sensei: we had sex with cloth on without me penetrating my partner
Friend: Wooow so now youre only half a virgin!