1) the act of being non-participatory during sex; i.e., just laying there while you're getting fucked. (This applies to both genders.)
2) While offering someone a high five, when the other person goes for the high five, you quickly put the top of your hand down touching the bottom of your hand and yell
deadfish1) he just laid there and didn't do anything. He was completely deadfish." "I don't really like having sex with him, so I deadfish hoping he won't like it."
2) "When our team scored a touchdown, I deadfished my friend by completely faking my high five."