The white knight incarnate; a person whose irrepressible compulsion to cockblock is the only salvation of womankind. If he isn't there to prevent it, women are powerless to defend themselves against the predatory motivations of all other members of his gender. Called so because of his astounding ability to block any cock currently known to man.
Bro: Dude, Alex is such a cockblock.
Brah: Yeah, he's a regular Stonewall Johnson.
Bro: Weird, I coulda sworn he got RB's all up in that shit.