When performing cunnalingus (oral stimulation of the vulva or clitoris) on a woman who is on her menstrual cycle.
I went down on my wife last night when she was on her period. And I came up looking like I just won a no handed spaghetti eating contest.
When a male or female partner engages in cunnilingus on a female who is currently on her menstrual cycle. After making the female partner climax, the partner who performed the act then has a smear of red vaginal discharge on their face.
Dude, what is that stuff on your face! You look like you've been in a no handed spaghetti eating contest!