The term "bored shitless" stems from homosexual ways. Where ones man anus can be penetrated so hard he can be void of all fecal matter, and thus bored.
adj. used as an expression "pissed shitless," referring to being so angry as to cause the spasming of one's sphincter muscles, causing the bowels to release and resulting in the defecation of one's pants.
Guy 1: Remember when that waiter got your order wrong and you yelled at him?