When a man and woman have sex in a pool and the man pulls out at the last second and shoots his "jellyfish" into the water. This can and should be enhanced by being performed at night in a pool with lights making the jellyfish glow. This move can also be performed with gay males, or even a solo male.
1. I came by your house last night to use your pool. I ended up giving your sister a jellyfish.
2. I jellyfished your sister.