When a man's semen ends up on his stomach, either by his own handywork or with the help of another; inspired by the species' method of reproductive development wherein the male carries the embryos on his stomach region.
I didn't have any tissues near by so i just seahorsed myself and passed out.
She doesn't like to swallow, so she usually just gives me the ol' seahorse.
A guy who is totally smitten with a girl. If a guy really likes a girl, then he is said to want to have her babies like a seahorse. (Much like if a girl really likes a guy, it is said that she wants to have his babies.)
"Yeah, we've been seeing each other for several months; this guy is totally my seahorse"