"shitting on the cock" means you disappointed someone by failing to fulfill the hopes they had for you. It is usually used between friends to make fun of each other.
it comes from the brazilian expression "cagar no pau".
-"I spent the whole night wingmaning for my friend Matt "Semen" and had to entertain his crush's friend for hours and he still lost her to a random guyin the club... I'm tired of him always shitting on the cock like that"
-"I know... I've grown used to it by now"
(v) When a friend or another male interferes with your interaction with an girl. Usually by bringing the attention to himself by boasting or other means. Frequently occurs when the other male is jealous of your progress; an extremely douchey form of cockblock
John: So I finished that book you were telling me about