The red flute is the process by which a male or female, preferably female, prepares to give a male a blowjob. Before the suck fest begins, the partner takes a razor blade and cuts a small slit on the scrotum at the base of the penis. The partner then proceeds to give the male a blow job and blows fairly hard on their penis and down the urethra. After blowing, blood and semen should spew from the incision on the scrotum and out the pee hole, creating a red flute.
Also note that the partner can also penetrate the penis with a thumb tack along the shaft of the penis while it is erect. While engaged in the red flute, the partner giving the red flute can put his or her fingers over the holes of the penetrated penis and make motions of playing a flute, creating different variations of sound.
Dude, last night with Linda was amazing. She was suckin my dick and right before i nutted, she whipped out the razor and gave me a red flute. I still have the stiches to prove it!