This is when you take
a small trash bag and place it over your partner's head when you're taking her from
behind, then you close
off the bag around her neck
as you pull out of her vagina and go balls deep into her anus, she will expel an enormous amount of air to inflate the trash bag to resemble a Jelly Fish.
Dude, I went
so far in her, so fast, she inflated the bag and looked
like the Man-a-War Jelly Fish