In broadcasting or sound engineering, redlining is when the levels are set too high and the lines on the screen/board are in the red instead of the more desired orange or yellow. Leaving levels at this high level may cause your audio to sound distorted and unpleasant.
The act of intertwining the penises of two (gay) men presumably during sex, similar to the two snakes on a caduceus or (as the name suggests) the twisted licorice in Red Vines.
"What is it called when two gay men intertwine their penises? Like the two snakes on the medical stick? Is it called redvining?" -Angela Martin from The Office (Season 9, Episode 8)