A made up sexual act which involves Partner A wearing a strap on dildo
on their forehead and then proceeds to have intercourse using said dildo
with Parter B. This was referenced in a Most Offensive Video Over-Dub of a Charlie Brown and Peanuts cartoon.
"We're going to do the Screw-Nicorn trick. That's when I put a dildo on my head and fuck Marcy headfirst like a Unicorn on amphetamines."