Despite sounding like a rough burger you might pick up at your favourite hang out, mcjizzy is a term used to describe the act of getting in with a friend and due to overexcitement and loss of control, jizzing your pants.
"She stuck her tongue down my throat, and left me in a right Mcjizzy moment"
The creamy 'sauce' used to flavor the Fillet O'Fish at McDonalds. In reality, that 'sauce' is just the semen of a sexually deprived employee, usually male, working in the hot, sweaty, back stoves. Usual characteristics are an abundance of zits, quite skinny in body mass and has an obsession with Star Wars and Star Trek.
Yeah, I just made a new batch of McJizz for the Fillet O'Fishes...Barney, you're up next, better get cracking, these things are going fast...seems to be a hit with the women...