1) a transitive verb, only applicable to males, used to describe the act of kicking, hitting, or otherwise causing injury to the groin, specifically the testicles (balls). usually used in the past tense (coiked)
see also knackered
2) a noun describing the unique and unmistakable pain associated with being hit in the testicles, (uncommon)
1) "My little brother was giving me the shits so i coiked him in the balls"
"I slipped on the balance beam and coiked myself"