After fellatio is performed on a male, the male stikes his female partner in the nose, causing the blood running from her nose to mix with the semen in on her lips, giving the appearance of her having consumed a strawberry milkshake.
When having sex with a menstruating woman, the penis is pulled out just prior to ejaculation, then manually ejaculated into the pool of smelly blood on the sheet. The resulting mixture is known as a "Strawberry Milkshake"