The Sperm (2007)

Sutin, a teenage rock musician, masturbates gleefully, and often. Way too often. One night, flying sperm escape and impregnate local women. The babies grow into an army of little creatures with the teen's head -- and libido. Not only do the nasty little monsters think only of chicks and jerking off, they also have a distressing tendency to die at the moment of ejaculation. The city really starts to panic when aliens accidentally turn one of the spawn into a giant.