shit·less 
(shĭtlĭs)
(shĭtlĭs)adj.
Vulgar Slang
Vulgar Slang
Used to intensify a verb with a personal object or a past participle modifying a personal noun or pronoun: scared him shitless; was bored shitless.
[From the reflex of involuntary defecation that can result from extreme terror.]